List of idioms of improbability

In English

Events that can never happen

• As a response to an unlikely proposition, "when pigs fly", "when pigs have wings", or simply "pigs might fly".
• "When Hell freezes over" and "A cold day in Hell" are based on the understanding that Hell is eternally an extremely hot place.
• The "Twelfth of Never" will never come to pass.
• "On Tibb's Eve" refers to the saint's day of a saint who never existed.
• "When two Sundays come together"
• "If the sky falls, we shall catch larks" means that it is pointless to worry about things that will never happen.
• "On the thirtieth of February", impossible in the Gregorian or Julian calendar, although it did occur in the Swedish calendar of 1712.

  Events that rarely or might never happen

• "Once in a blue moon" refers to a rare event.
• "Don't hold your breath" implies that if you hold your breath while waiting for a particular thing to happen, you will die first.
• Having to wait for something "until the cows come home"

  Tasks that are difficult or impossible to perform

• To have "a snowball's chance in Hell".
• "Like getting blood from a stone", and "like squeezing water from a stone".
• "Like finding a needle in a haystack"
• "Like herding cats"
• "Squaring a circle"

  Things that are impossible to find

• "As rare as hen's teeth".
• "As rare as rocking-horse poo".

  In other languages

• Afrikaans – as die perde horings kry
• Albanian – ne 36 gusht
• Arabic has a wide range of idioms differing from one region to another. In some Arab countries of the Persian Gulf, one would say إذا حجت البقرة على قرونها idha ḥajjit il-bagara `ala gurunha. In Egypt, one says في المشمش fil-mishmish. Other Arab people, mainly Palestinian, use the expression لما ينور الملح lemma ynawwar il-malḥ, which roughly translates into "when salt blossoms" or "when salt flowers" In Gulf or Khaleeji Arabic is the expression يوم الديك يبيض or "when the rooster lays an egg".
• Breton – Pa nijo ar moc'h
• Bulgarian – the three most common phrases are: когато цъфнат налъмите, на Върба в сряда/петък and на куково лято. A related phrase, през крив макарон has a similar meaning, usually used as a threat to have a privilege taken away.
• Chinese – 太陽從西邊升起
• Czech – až naprší a uschne, Another expression is až opadá listí z dubu. Another is na svatého Dyndy, Dyndy being a fictional saint whose name rhymes with jindy or with nikdy.
• Danish – når der er to torsdage i én uge
• Dutch – met, or als Pinksteren en Pasen op één dag vallen
• Esperanto – je la tago de Sankta Neniamo — a loan-translation from German.
• Finnish – sitten kun lehmät lentävät - when the cows fly. Also jos lehmällä olisi siivet, se lentäisi, implying futile speculations. Also kun lipputanko kukkii and Tuohikuussa Pukin-päivän aikaan. Sometimes also kun Helvetti jäätyy, although saying it aloud to someone is considered very rude and hostile.
• French – à la Saint-Glinglin. Glinglin is a nonsense rhyme for the French word saint. A couple of other expressions are quand les poules auront des dents and quand les coqs pondront des œufs. An expression, today falling into disuse, is la semaine des quatre jeudis, as in "that will happen during the week of the four Thursdays". The expression aux calendes grecques was also used for indefinite postponement, derived from the ancient Latin expression. To express logical impossibility: si ma tante en avait, on l'appellerait mon oncle. What she would have is left to the imagination, and it is probably a parallel creation rather than a borrowing to or from Marathi. To express someone's wishful thinking: Il attend que les alouettes lui tombent toutes cuites dans la bouche.
• German – Wenn Schweine fliegen können! is identical to the English saying "when pigs fly", although the older proverb Wenn Schweine Flügel hätten, wäre alles möglich is in more common use, often modified on the second part to something impossible, like "if pigs had wings, even your idea might work". Another phrase is Am Sankt-Nimmerleins-Tag. Wenn Weihnachten und Ostern auf einen Tag fallen!
• Georgian – როცა ვირი ხეზე ავა
• Greek – του Αγίου Ποτέ is sometimes used, although some people may prefer the profane Του Αγίου Πούτσου ανήμερα. One might also say that an unlikely event will happen "on the 32nd of the month". To express indefinite postponement, you might say that an event is deferred "to the Calends". A less common expression used to point out someone's wishful thinking is Αν η γιαγιά μου είχε καρούλια, θα ήταν πατίνι.
• Hebrew – כשיצמחו שיערות על כף ידי. Another is a legal term, referring to the indefinite postponing of a case, "until Elijah comes".
• Hindi – सूरज पश्चिम से उगा है and बिन मौसम की बरसात. The latter is also used to denote something unexpected/untimely as much as improbable.
• Hungarian – The two most often used expressions are majd ha piros hó esik, and majd ha cigánygyerekek potyognak az égből. There is a third, uncommonly used phrase: majd ha fagy, the short version of majd ha a pokol befagy. A couple of other expressions are holnapután kiskedden and soha napján.
• Italian – quando gli asini voleranno, il 31 febbraio, il giorno di "mai" ed il mese di "poi", dopodomai and, similarly to Latin, alle Calende greche. To imply futile speculations, common expressions are se mia nonna avesse le ruote, sarebbe una carriola or se mio nonno avesse avuto tre palle, sarebbe stato un flipper.
• Japanese – "You can't catch wind in a net." Another idiom of improbability is which means "finding clams in a field".
• Latin – ad kalendas graecas signified indefinite postponement, since the Greek calendar had no Calends period; also cum mula peperit = "when a mule foaled".
• Korean – 해가 서쪽에서 뜨겠다 means "the sun might rise from the West", commonly used as a response to a news that something improbable happened.
• Lombard – quand pìssen i òch, refers to the fact that geese do not urinate.
• Malay – menunggu kucing bertanduk
• Malayalam – കാക്ക മലർന്നു പറക്കും, " crow will fly upside down"
• Marathi – आत्याबाईं ना मिश्या असत्या तर काका म्हंटले असते, "if aunt grows moustaches she would be called uncle"
• Norwegian – når helvete fryser til is or når helvete frys til is
• Persian – وقت گل نی, "when the reed plant blossoms"
• Piedmontese – smana dij tre giòbia.
• Polish – na święty Nigdy ; zobaczysz... jak świnia niebo – refers to the pigs' anatomical inability to raise their head and look at the sky; prędzej mi kaktus na dłoni wyrośnie ; Jedzie mi tu pociąg?.
• Portuguese – no dia de São Nunca, nem que a vaca tussa, quando os porcos voarem and quando as galinhas tiverem dentes. In Brazilian Portuguese, especially in the historical context of World War II, Brazilian Expeditionary Force#Nickname, which has since reversed meaning, given the participation of Brazil in the war.
• Romanian – la Paștele cailor/la Ispas, când o face plopul pere și răchita micșunele, la Sfântul Așteaptă, când va zbura porcul, and la pulivară.
• Russian – когда рак на горе свистнет, "when the crawfish whistles on the mountain". После дождичка в четверг, literally "after the rain on Thursday" yet meaning never. Не видать как своих ушей, "not to see like your ears".
• Scottish Gaelic – pàillean am fàsach, "a palace in a wilderness"
• Serbo-Croatian – кад на врби роди грожђе, "when willow bears grapes". Another variant is кад на врби засврби, "when willow get itchy". Note rhyme in vrbi zasvrbi. Мало сутра, literally "a little bit tomorrow", has a similar meaning as "all my eye".
• Seychellois Creole, also known as Kreol or Seselwa – lannen de mil zanmen is used, which means "year two thousand and never". It is a fairly new expression used mainly among the youth.
• Slovene – Ob svetem Nikoli is a wordplay that literally means "on St. Nicholas' feast day". The word nikoli, when stressed on the second syllable, means "never", when stressed on the first it is the locative case of Nikola, i.e. Nicholas.
• Spanish – cuando las vacas vuelen or cuando los cerdos vuelen. Its most common use is in response to an affirmative statement, for example "I saw Mrs. Smith exercising, I swear!" to which the response given would be something like, "Yeah right, and cows fly". Other variations slightly fallen into disuse include cuando las ranas crien pelo and cuando San Juan agache el dedo. The latter is a reference to the common depiction of St. John with one or two extended fingers.
• Tagalog – . There is euphony between the nouns and.
• Turkish – balık kavağa çıktığında. Another one is çıkmaz ayın son Çarşambasında. A very popular one is Eşek sudan gelince
• Ukrainian – коли рак на горі свисне, "when the crawfish whistles on the mountain"; or a longer variant коли рак на горі свисне, а риба заспіває, "when the crawfish whistles on the mountain and fish sings". Other expressions are: не бачити тобі... як своїх вух ; на кінський Великдень.
• Welsh – tan ddydd Sul y pys and pan fydd yr Wyddfa'n gaws. More modern additions include pan fydd moch yn hedfan, pan fydd uffern yn rhewi drosodd and pan fydd 'Dolig yn yr haf, a gwsberis yn y gaeaf. Rare events meaning "once in a blue moon" include: unwaith yn y pedwar amser and unwaith yn y pedwar gwynt.