worsen v.

Old English wiersa, wyrsa "worse," from Proto-Germanic *wers-izon- (source also of Old Saxon wirs, Old Norse verri, Swedish värre, Old Frisian wirra, Old High German wirsiro, Gothic wairsiza "worse"), comparative of PIE *wers- (1) "to confuse, mix up" (source also of Old High German werra "strife," Old Saxon werran "to entangle, compound;" see war (n.)). Used as a comparative of bad, evil, ill or as the opposite of better. The adverb is Old English wyrs; the noun is Old English wyrsa. Phrase for better or for worse is attested from late 14c. (for bet, for wers); to change for the worse is recorded from c. 1400.

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.