Used in collocation, jot and tittle denote every tiny detail; both words mean a very small amount.

For example, Richard Delong concluded Dissent, with respect, is always worth it, published in the Lancaster Eagle-Gazette (Lancaster, Ohio) on 17^th September 2017, with these words:

The courage of one’s convictions indicates maturity. Rejecting all who dare disagree shows immaturity. The person who insists that only those who agree in every jot and tittle can remain in the circle of friends should not prepay for a large funeral room. One who unfriends others so easily will likely be unfriended in spades before this life ends.

This collocation originated in Jesus’s Sermon on the Mount in the gospel of Matthew, 5:18:

(King James Version – 1611)
For verily I say vnto you, Till heauen and earth passe, one iote or one title, shall in no wise¹ passe from the law, till all be fulfilled.

(¹ in no wise: by no means)

Via Latin iōta, jot is from Greek ἰῶτα, the name of the letter ι, Ι, the ninth and the smallest in the Greek alphabet, transliterated as i, I (Spanish jota, from iōta, is the name of the letter j, J). The Early Version (around 1382) of the Wycliffe Bible mentions in Matthew, 5:18, the fact that this letter is the smallest:

Forsothe I say to ȝou trewthe, til heuen and erthe passe, oon i, `that is leste lettre, or titil², shal nat passe fro the lawe, til alle thingis be don.

(² in contemporary English: one i, that is the least letter, or tittle)

The noun jot, which primarily denotes the least letter or part of a writing, came to mean, generally, the very least, or a very little, part, point or amount. For example, in The most excellent Historie of the Merchant of Venice (Quarto 1, 1600), by the English poet and playwright William Shakespeare (1564-1616), Portia, disguised as “a young and learned Doctor”, says to Shylock:

– Portia. A pound of that same Merchants flesh is thine,
the Court awards it, and the law doth giue it.
– Shylock. Most rightfull Iudge.
– Portia. And you must cut this flesh from off his breast,
the law alowes it, and the court awards it.
– Shylock. Most learned Iudge, a sentence, come prepare.
– Portia. Tarry a little, there is some thing else,
this bond doth giue thee heere no iote of blood,
the words expresly are a pound of flesh:
take then thy bond, take thou thy pound of flesh,
but in the cutting it, if thou doost shed
one drop of Christian blood, thy lands and goods
are by the lawes of Venice confiscate
vnto the state of Venice.

The noun tittle, originally the same word as title, is from Latin tĭtŭlus, denoting a superscription, an inscription, a label, the name of a book, also a placard or notice that a thing is to be sold or let, and a title of honour.

The primary sense of tittle is a small mark used in writing or printing. The formulation of Matthew, 5:18, in the New International Version (2011) reflects this:

For truly I tell you, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished.

(The noun tittle was also a term specific to horn-books—cf. How hornbooks are at the origin of ‘criss-cross’.)

From its literal sense, tittle came to mean figuratively the smallest, or a very small, part of something, and a tiny amount.

Also from Latin tĭtŭlus, the Spanish word tilde denotes the accent ~ placed over n when pronounced ny, as in señor, and the Portuguese word til denotes the same accent placed over a or o when nasalised, as in São Paulo.