Abbott-Smith Manual Greek Lexicon
βαπτισμός (G909)
4 *† βαπτισμός , -οῦ, ὁ ( βαπτίζω ) , prop., the act of which βάπτισμα is the result; a dipping , washing , lustration : Mk 7:4 ; of Jewish ceremonial, He 9:10 ; in He 6:2 , βαπτισμῶν διδαχήν ( -ῆς ), "the pl. and the peculiar form seem to be used to include Christian baptism with other lustral rites" (Westc, in l.). baptism : FlJ, Ant., 18, 5, 2 (of John's baptism), and some Fathers (v. Soph., s.v.). Not so in NT, unless ἐν τ. βαπτισμῷ , in the act of baptism , Col 2:12 , be read with Tr. (Rec., WH, R, -ματι ).†
G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain