taun.

Etymology: < classical Latin tau (in post-classical Latin also thau (Vulgate): compare note), name of the letter T in the Greek alphabet, in post-classical Latin also used with reference to the shape of Christ's cross (late 2nd cent. in Tertullian) and as name of the last letter of the Hebrew alphabet (4th cent.) < ancient Greek ταῦ , name of the letter T in the Greek alphabet < Phoenician tw (probably tāw ): see further at T n. Compare Middle French thau , Middle French, French tau (1355 in the passage translated in quot. a1475, earliest in sense 1a). Compare taw n.¹In early use in sense 1 frequently with reference to marks or signs in the Old Testament and Hebrew Scriptures interpreted as allegorically prefiguring the Cross. Although such use ultimately refers to the Hebrew Scriptures, the passages in question (e.g. in Genesis, with reference to Cain's mark, and in Exodus (compare quots. OE, a1400¹), with reference to the mark which the Israelites put on their doorposts before the night of Passover) use formally and etymologically different words for ‘sign, mark’. In comparable Latin exegetical passages the Greek and the Hebrew letter are not clearly distinguished; in Tertullian the Greek letter is referred to, while other later discussions refer to the Hebrew letter or to both. In use in discussions specifically of Ezekiel 9:4 (as e.g. quots. a1475, 1564 at sense 1a) after post-classical Latin thau (4th or 5th cent. in this sense in St Jerome Commentary on Ezekiel 3. 9, apparently immediately after Hellenistic Greek θαῦ (first half of the 3rd cent. ad in Origen Selecta in Ezechielem 13. 800. 50 ff.)) and its model Hebrew tāw ‘mark, sign’ (Ezekiel 9:4, 6; also in Job 31:35 in sense ‘signature’), of uncertain origin, but identified with the homonymic letter name early on. With sense 4 compare scientific Latin tau , specific name (1758 of a moth, 1766 of a fish, 1781 of a fly, 1792 of a beetle). In sense 5 after French tau (1847, in the passage translated in quot. 1855, or earlier in this sense). In senses 6a and 6b with allusion to the initial letter of ancient Greek τρίτος third (see trito- comb. form); with the semantic motivation, compare quots. 1949² at sense 6a, 1977¹ at sense 6b. In sense 7 with allusion to the initial letter of tubule n.; compare quot. 1975. In Compounds 2 after German τ-Fraktion (T. Bülcher et al. 1952, in Klin. Wochenschr. 1 Apr. 329/1).