Lexical Definition

‎βαπτισμός‎ baptismós (bap-tis-mos') baptism ^G:N-M
from ‎βαπτίζω‎

baptism, washing.

• ablution (ceremonial or Christian)

Abbott-Smith

*† βαπτισμός, -οῦ, ὁ (< βαπτίζω) , prop., the act of which βάπτισμα is the result;
1. 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.).
2. 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).†

Abbott-Smith References

Liddell-Scott-Jones

βαπτισμός-ισμός, ὁ,

dipping in water, immersion, [NT+2nd c.AD+]

__2 metaphorically, εἰς κακίας β. οἰχήσεται [Refs]
__3 lethargic sleep, Archig.and [Refs 2nd c.BC+]
__4 baptism, [Refs 1st c.AD+]

_{LSJ Scripture Refs: Mark.7.4 ☩ Heb.9.10}