relent (v.) Look up relent at Dictionary.com
late 14c., "to melt, soften, dissolve," from re- + Latin lentus "slow, viscous, supple" (see lithe), perhaps on model of Old French rallentir. Sense of "become less harsh or cruel" first recorded 1520s. The notion probably is of a hard heart melting with pity. Related: Relented; relenting.