στρατεύω and depon. -ομαι, so always in NT

(στρατός, an encamped army), [in LXX for מההּ hith. יָצָא, צָבָא; metaphorically, 4Ma.9:23 ;]

used of the general, to make war, do battle, and (chiefly) of the soldiers serving under him, to serve as a soldier: Luk.3:14, 1Co.9:7, 2Ti.2:4. Metaphorical (cf. MM, ii, xxiii), of spiritual conflict, to war, make war: 2Co.10:3, 1Ti.1:18, Jas.4:1, 1Pe.2:11.†

(AS)

to make war, do battle; to serve as a soldier; to war, make war