mid-15c., "to adjust or settle by mutual concessions," also intransitive, "to make a compromise," from compromise (n.). Meaning "expose to risk or hazard, endanger the reputation of" is from 1690s. Also formerly in the same sense was compromit (early 15c.), from Latin compromittere. Related: Compromised; compromising.

"to pledge, engage by solemn promise" (obsolete except in archaic plight one's troth), Middle English plighten, from Old English pligtan, plihtan "to endanger, imperil, compromise," verb form of pliht (n.) "danger, risk" (see plight (n.2)), from Proto-Germanic *plehti-, which ultimately is perhaps from PIE root *dlegh- "to engage oneself, be or become fixed," or else a substratum word. The notion is "to put (something -- honor, troth) in danger or risk of forfeiture;" it is rarely used of physical things. Related: Plighted; plighting.