before 900;Middle English;Old Englishthrēo, thrīo, feminine and neuter of thrī(e); cognate with Dutchdrie,Germandrei,Old Norsethrīr,Gothicthreis,Greektreîs,Latintrēs three, ter thrice, Irishtrí, OCS tri,Sanskrittrī, tráyas
O.E. þreo, fem. and neut. (masc. þri, þrie), from P.Gmc. *thrijiz (cf. O.Fris. thre, M.Du., Du. drie, O.H.G. dri, Ger. drei, O.N. þrir, Dan. tre), from PIE *trejes (cf. Skt. trayas, Avestan thri, Gk. treis, L. tres, Lith. trys, O.C.S. trye, Ir., Welsh tri "three"). 3-D first attested 1952, abbreviation of three-dimensional (1878). Three-piece suit is recorded from 1909. Three cheers for ______ is recorded from 1751. Three-martini lunch is attested from 1972. Three-ring circus first recorded 1898. Three-sixty "complete turnaround" is from 1927, originally among aviators, in ref. to the number of degrees in a full circle. Three musketeers translates Fr. les trois mousquetaires, title of an 1844 novel by Alexandre Dumas père.