Henry George Liddell, Robert Scott, A Greek-English Lexicon

A.“τριοῖσι” Hippon. 51, and “τρίεσσι” Delph.3(5).80.21 (iv B. C.); Aeol. “τρίσσι” Inscr.Perg. 245 B18 (Pitana): acc. τρεῖς (written τρες IG12.24.16, 44.15, 188.37, 1085, al.), τρία: Dor. nom. “τρέες” Leg.Gort.9.48; “τρῆς” IG12(3).1640 (Thera); “τρῖς” SIG236A10 (Delph., iv B. C.), Tab.Heracl.1.23; acc. “τρίινς” Leg.Gort.5.54, al. (for Τρίνς, lengthd. to correspond with the other cases); “τρῖς” IG12.838,839 (vi B. C.), SIG239 D ii 28 (Delph., iv B. C.), Berl.Sitzb.1927.158 (Cyrene):—three, Il.15.187, etc.; τρία ἔπεα three words, prov. in Pi.N.7.48,—for from the earliest times three was a sacred and lucky number, esp. with the Pythagoreans (cf. τριάς), Arist.Cael.268a11; so “τῶν τριῶν μίαν λαβεῖν εὔσοιαν” S.Fr.122; εἰ καὶ τῶν τριῶν ἓν οἴσομαι ib.908; cf. “σωτήρ” 1.2:—διὰ τριῶν ἀπόλλυμαι I am thrice, i. e. utterly, undone, E.Or.434 (cf. τριάζω）; ἡ διὰ τριῶν ἀγωγή the 'trivium', Simp. in Ph.1171.34; “ἵνα δήσῃ τρία τρία” by threes, POxy.121.19 (iii A. D.). (I.-E. stem tr[icaron]-, fuller form trey-, nom. tréy-es (Skt. tráyas, Lat. tres), whence τρέες, contr. τρῆς and τρεῖς (written τρες IG12.295.11); acc. tri-ns (Goth. prins, Skt. tr[imacracute]n), whence τρῖς and τρίινς; in Gr. the nom. τρεῖς functions as acc. (as in Att.), or the acc. τρῖς as nom. (ll. cc.).)