Other forms: untied, unties, untying
To untie is to undo a knot. Untie the rope, untie your laces, untie the boat.
It is the direct opposite of tie, and the un- prefix here means reversing an action rather than simply not doing it — which is the same un- as in undo, unlock and unpack. The present participle is untying and the past is untied. Note untie the boat, which means to cast off; and that in English un- attaches to verbs to reverse them and to adjectives to negate them, which are two different jobs.
1verbuntieTo undo a knot.
“It took about ten minutes to untie a knot that took four seconds.”
untie is an undoing.
Old English untigan is un- plus tigan, to tie. The reversing un- is one of the oldest prefixes in English and is entirely native, which is why it attaches so easily to plain everyday verbs.
Old English
untīġan — to untie
Middle English
untien
English, today
untie
From Middle English untien, unteyen, untyȝen, untiȝen, from Old English untīġan (“to untie”), equivalent to un + tie.
Etymology from Wiktionary, CC BY-SA