Thorn with stroke

Ꝥ, or Þ (thorn) with stroke was a scribal abbreviation common in the Middle Ages. It was used for, as well as, the -þan/-ðan in síðan, þat, þæt, and þess. In Old English texts, the stroke tended to be more slanted, while in Old Norse texts it was straight. In Middle English times, the ascender of the þ was reduced, which caused the thorn with stroke abbreviation to be replaced with a thorn with a small t above the letter.
Unicode encodes Ꝥ as, and ꝥ at.
A thorn with a stroke on the descender also exists, used historically as an abbreviation for the word "through". The codepoints are, and.