Old English heawan "to chop, hack, gash" (class VII strong verb; past tense heow, past participle heawen), earlier geheawan, from Proto-Germanic *hawwan (cf. Old Norse hoggva, Old Frisian hawa, Old Saxon hauwan, Middle Dutch hauwen, Dutch houwen, Old High German houwan, German hauen "to cut, strike, hew"), from PIE root *kau- "to hew, strike" (cf. Old Church Slavonic kovo, Lithuanian kauju "to beat, forge;" Latin cudere "to strike, beat;" Middle Irish cuad "beat, fight").
Weak past participle hewede appeared 14c., but hasn't displaced hewn. Seemingly contradictory sense of "hold fast, stick to" (in phrase hew to) developed from hew to the line "stick to a course," literally "cut evenly with an axe or saw," first recorded 1891. Related: Hewed; hewing.