un- + tie

source: [恵が髪をはらりと解くGIF画像｜無料GIF画像検索 GIFMAGAZINE 484693]

verb (unties, untying, untied) with object

undo or unfasten (a cord or knot):

〈結んだ物など〉をほどく, 解く; 〈包みなど〉のひもをほどく

e.g. she knelt to untie her laces.

undo a cord or similar fastening that binds (someone or something):

〈つながれた動物など〉を解放する, 解き放す.

e.g. Morton untied the parcel.

Old English untīgan(see un-2, tie).