Usage: 5 forms in 5 verses
Form Translated As     In Verse(s)
ἐγκαυχᾶσθαι to greatly boast 2Thess.1.4
ενεκαυχήσαντο boasted LXX.Ps.74.4
εγκαυχώμενοι ones boasting LXX.Ps.97.7
εγκαυχάσθαι to boast LXX.Ps.106.47
εγκαυχά do you boast LXX.Ps.52.1

Liddell-Scott-Jones

ἐγκαυχάομαι (egkauchaomai) to boast of G:V

ἐγκαυχάομαι,

pride oneself on, ἔν τινι [LXX+5th c.BC+]

LSJ Scripture Refs: LXX.Ps.73.4*