Abbott-Smith Manual Greek Lexicon
χξϛʹ (G5516)
1 (KJV) χξϛʹ (on ς , v.s. Ζ ), in T, Tr., Rec. for ἑξακόσιοι ἑξήκοντα ἕξ , six hundred and sixty-six (L, mg., R, mg., six hundred and sixteen ), the mystical number of the Beast: Re 13:18 (on the interpretation, v. Swete, Ap. , 172 f.).†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain