expression, godan verb (-ku)
undo a knot; untie a knot
Literal action of untying a knot. The expression is a straightforward verb phrase.
靴ひもの結び目を解くのに手間取った。
I had trouble untying the knot in my shoelaces.
彼はロープの結び目を解いて、荷
He untied the knot in the rope and unpacked the luggage.