soften (v.)

late 14c., "to mitigate, diminish" (transitive), from soft (adj.) + -en (1). Meaning "to make physically soft" is from 1520s; intransitive sense of "to become softer" is attested from 1610s. Soften up in military sense of "weaken defenses" is from 1940. Related: Softened; softening.