Strong's Greek Concordance

G3166: μεγαλαυχέω

megalauchéō · “to boast”

Definition

akin to G837 (αὐξάνω) and G2744 (καυχάομαι)); to talk big, i.e. be grandiloquent (arrogant, egotistic)

KJV translates it as: boast great things

Word origin: from a compound of G3173 (μέγας) and (to boast;

Extended definition

μεγαλ-αυχέω, -ῶ (= μεγάλα αὐχέω)
[in LXX: Eze.16:50 (גָּבַהּ), al. ;]
to boast great things: Jas.3:5 (Rec. for μεγάλα αὐχεῖ, WH).†
(AS)

Abbott-Smith Manual Greek Lexicon (1922) via STEPBible TBESG (CC BY 4.0).