ripen v.

Old English ripe, of grain, fruit, seed, a field, "ready for reaping, mature," of animals used as food, "fit for eating," from West Germanic *ripijaz (source also of Old Saxon ripi, Middle Dutch ripe, Dutch rijp, Old High German rifi, German reif); related to Old English repan "to reap" (see reap).

Usually explained as "fit for reaping," in which case it would have been originally of grains and extended to all fruit. Figurative use by c. 1200. As "full-grown, developed, finished" (a ripe age) by late 14c. The meaning "ready for some action or effect" (as in the time is ripe) is from late 14c. Of lips, the mouth, "round and full, like ripe fruit," by 1580s. Related: Ripely. The proverb soon ripe, soon rotten is attested by 1540s.

word-forming element making verbs (such as darken, weaken) from adjectives or nouns, from Old English -nian, from Proto-Germanic *-inojan (also source of Old Norse -na), from PIE adjectival suffix *-no-. Most active in Middle English and early modern English, hence most verbs in -en are comparatively recent.