Middle English word forwaxen comes from Old English weaxan (To increase. To wax, grow.), Old English for-

Detailed word origin of forwaxen

Dictionary entry	Language	Definition
weaxan	Old English (ang)	To increase. To wax, grow.
for-	Old English (ang)	Forming verbs from verbs with various senses especially ‘wrongly, away from, astray, abstention, prohibition, perversion, destruction’. Used to create intensified adjectives and verbs from other adjectives and verbs, with the sense of completely or fully. Compare Modern English use of up. Very.
forweaxan	Old English (ang)	To overgrow, swell, grow too much; wax wrongly; grow away.
forwaxen	Middle English (enm)

Words with the same origin as forwaxen