jot n.

"very small amount," 1630s, figurative use of iota, ninth and smallest letter in the Greek alphabet (corresponding to Latin -i-). Its use in this sense is after Matthew v.18 (see jot (n.), which is the earlier form of the name in English), but iota in classical Greek also was proverbially used of anything very small. The letter name is from Semitic (compare Phoenician and Hebrew yodh).

"small stroke or point in writing," late 14c. (Wycliffe, in Matthew v.18), translating Latin apex in Late Latin sense of "accent mark over a vowel," which itself translates Greek keraia (literally "a little horn"), used by the Greek grammarians of the accents and diacritical points, in this case a Biblical translation of Hebrew qots, literally "thorn, prick," used of the little lines and projections by which the Hebrew letters of similar form differ from one another.

Wycliffe's word is borrowed from a specialized sense of Latin titulus (see title (n.)), which was used in Medieval Latin (and in Middle English and Old French) to indicate "a stroke over an abridged word to indicate letters missing" (and compare Provençal titule "the dot over -i-").

As apex was used by the Latin grammarians for the accent or mark over a long vowel, titulus and apex became to some extent synonymous; hence Wyclif's use of titil, titel to render L. apex [OED]

Compare tilde, which is the Spanish form of the same word.