c. 1300, "confessing oneself to be overcome or vanquished," from Old French recreant "defeated, vanquished, yielding, giving; weak, exhausted; cowardly," present-participle adjective from recroire "to yield in a trial by combat, surrender allegiance," literally "believe again;" perhaps on notion of "take back one's pledge, yield one's cause," from re- "again, back" (see re-) + croire "entrust, believe," from Latin credere (see credo).
Non sufficit ... nisi dicat illud verbum odiosum, quod recreantus sit. [Bracton, c. 1260]
Meaning "cowardly" in English is from late 14c. Meaning "unfaithful to duty" is from 1640s.