Translation guide
To undo or release something that is fastened, such as a button, buckle, belt, or knot. The most common Japanese expressions depend on what is being unfastened.
To undo a button, snap, or similar small fastener, typically on clothing.
unfasten a button
unfasten a seatbelt
Means 'to take off' and can be used for detachable items like brooches or clip-on accessories.
unfasten a brooch
To undo a belt, buckle, or similar strap-like fastener.
To undo a knot, bow, or tied string.
To open or release a mechanical fastener like a lock, latch, or hook.
外す (hazusu) is the most versatile for unfastening things that are attached or hooked. 解く (hodoku) is specifically for untying knots or strings. 取る (toru) is for taking off detachable items. Use 外す when in doubt for buttons, belts, and clasps.
unfasten a necklace
unfasten a ribbon
開ける (akeru) means 'to open' and is not used for unfastening clothing. Use 外す for buttons and zippers, or 脱ぐ (nugu) for taking off clothes entirely.
ベルトを緩める
loosen/unfasten a belt slightly
靴ひもがほどけた
My shoelaces came unfastened.
錠を開ける
unfasten a lock (open it)