Sokuon

The sokuon is a Japanese symbol in the form of a small hiragana or katakana, as well as the various consonants represented by it. In less formal language, it is called 2=小さいつ or 2=小さなつ, meaning "small ". It serves multiple purposes in Japanese writing.

Appearance

In both hiragana and katakana, the appears as a reduced in size:

	Full-sized	Sokuon
Hiragana	つ	っ
Katakana	ツ	ッ

Use in Japanese

The main use of the is to mark a geminate consonant, which is represented in most romanization systems by the doubling of the consonant, except that Hepburn romanization writes a geminate ch as tch. It denotes the gemination of the initial consonant of the symbol that follows it.
Examples:
The sokuon never appears at the beginning of a word or before a vowel, and rarely appears before a syllable that begins with the consonants n, m, r, w, or y. In addition, it does not appear before voiced consonants, or before h, except in loanwords, or distorted speech, or dialects. However, uncommon exceptions exist for stylistic reasons: For example, the Japanese name of the Pokémon species Cramorant is ウッウ, pronounced.
The sokuon is also used at the end of a sentence, to indicate a glottal stop, which may indicate angry or surprised speech. This pronunciation is also used for exceptions mentioned before. There is no standard way of romanizing the sokuon that is at the end of a sentence. In English writing, this is often rendered as an em dash. Other conventions are to render it as t or as an apostrophe.
In the International Phonetic Alphabet, the sokuon is transcribed with either a colon-like length mark or a doubled consonant:

The sokuon represents a mora, thus for example the word consists of only two syllables, but four morae: ni-p-po-n.

Etymology

Major Japanese dictionaries list, as a synonym for sokuon. This suggests an origin in Middle Chinese phonology, where sokusei, also known as, referred to a checked tone, or a syllable that ends in an unreleased plosive. 促聲 contrasts with 舒聲 which is a syllable that ends in a vowel, semivowel, or nasal.
The Meiji-era linguist Ōshima Masatake used the terms sokuon and hatsuon to describe ending consonants in Chinese. These sounds were classified as "Labial consonant, "Coronal consonant and "guttural". Sokuon, in particular, were classified as follows: is the "labial plosive", is the "lingual plosive", and is the "guttural plosive". Another of Ōshima's descriptions even more explicitly related the terms sokuon and hatsuon to the four tones of Middle Chinese.
Modern Japanese sokuon arose, in no small part, from consonant assimilation that occurred when an Early Middle Japanese approximation of a Chinese sokuon, such as pu, t or ki/ku, was followed by an obstruent.

Use in other languages

In addition to Japanese, sokuon is used in Okinawan katakana orthographies to represent glottal or ejective consonants. Ainu katakana uses a small ッ both for a final t-sound and to represent a sokuon. As with tsu, sokuon’s katatana form can be used as an emoticon due to its similar appearance to the smile emoticon.

Computer input

There are several methods of entering the sokuon using a computer or word-processor, such as xtu, ltu, ltsu, etc. Some systems, such as Kotoeri for macOS and the Microsoft IME, generate a sokuon if an applicable consonant letter is typed twice; for example tta generates った.

Other representations

Computer encodings