A tittle is a small distinguishing mark, such as a diacritic or the dot on a lowercase i or j. The tittle is an integral part of the glyph of i and j, but diacritic dots can appear over other letters in various languages. The tittle of i or j is omitted when a diacritic is placed in the tittle's usual position (as í or ĵ), but not when the diacritic is elsewhere (as į, ɉ), and traditionally not in Vietnamese.
This word is rarely used. Its most prominent occurrence is in the introduction to the Antithesis of the Law in the Gospel of Matthew (5:18): "For assuredly, I say to you, till heaven and earth pass away, one jot or one tittle will by no means pass from the law till all is fulfilled" (NKJV). The quotation uses them as an example of extremely minor details. The phrase "jot and tittle" indicates that every small detail has received attention. The word tittle in this far older text refers, however, to the Hebrew sign, the tagin.
In the Greek original translated as English "jot and tittle" is found iota and keraia. Iota is the smallest letter of the Greek alphabet (ι), but since only capitals were used at the time the Greek New Testament was written (Ι), it probably represents the Hebrew or Aramaic yodh (י) which is the smallest letter of the Hebrew and Aramaic alphabets. "Keraia" is a hook or serif, possibly accents in Greek but more likely hooks on Hebrew or Aramaic letters, (ב) versus (כ), or additional marks such as crowns (as Vulgate apex) found in the Torah, the Five Books of Moses, which are the first five books of the Jewish Bible. A keraia is also used in Greek numerals.
The standard reference for NT Greek is A Greek-English Lexicon of the New Testament and other Early Christian Literature, Bauer, Gingrich, Danker, et al.
A number of alphabets use dotted and dotless I, both upper and lower case.
In the modern Turkish alphabet, the absence or presence of a tittle distinguishes two different letters representing two different phonemes: the letter "I" / "ı", with the absence of a tittle also on the lower case letter, represents the close back unrounded vowel [ɯ], while "İ" / "i", with the inclusion of a tittle even on the capital letter, represents the close front unrounded vowel [i].
In the latest Latin based Kazakh alphabet, there is also a dotted and dotless letter i and I for different sounds.
There is only one letter I in Irish; but i is undotted in the traditional uncial Gaelic script to avoid confusion of the tittle with the buailte overdot found over consonants. Modern texts replace the buailte with a h, and use the same antiqua-descendant fonts, which have a tittle, as other Latin-alphabet languages. However, bilingual road signs use dotless i in lowercase Irish text to better distinguish i from í. The letter "j" is not used in Irish other than in foreign words.
In most Latin-based orthographies, the lowercase letter i loses its dot when a diacritical mark, such as an acute or grave accent, is place atop the letter. However, in Vietnamese, the lowercase letter i traditionally retains its dot even when accented. This detail is often lost in computers and on the Internet, due to the obscurity of Vietnamese specialty fonts.