From Latin 'devotus' (vowed) — in Roman tradition, 'devotio' was a general vowing his own life to the gods for victory.
Deeply religious and committed to worship; totally committed to a cause or belief.
From Old French 'devot' (pious, devoted), from Latin 'devotus' meaning 'solemnly pledged, consecrated, given over by vow,' the past participle of 'devovere' (to vow away, to dedicate by a solemn vow), composed of the prefix 'de-' (down, away, completely) + 'vovere' (to vow, to dedicate to a deity). The Latin 'vovere' descends from PIE *wegwʰ- (to speak solemnly, to make a sacred vow), the same root that underlies English 'vow' and 'vote' (both from Latin 'votum,' a vow or desire directed at the divine). The Roman 'devotio' was a precise and extreme ritual act: a general, facing likely defeat, would formally
The Roman military ritual of 'dēvōtiō' was one of the most dramatic acts in ancient warfare: a general would formally vow his own life to the gods of the underworld, then charge into the enemy lines to die, believing his death would bring divine victory to his army. 'Devout' literally carries the meaning of self-sacrifice.