To make loose; undo:
To relax is defined as to become calm, to loosen, or to calm down.
To make or become slower; slow down:
(Economics) To make money harder to borrow or obtain.
Find another word for untighten. In this page you can discover 8 synonyms, antonyms, idiomatic expressions, and related words for untighten, like: ease, let up, loose, loosen, relax, slack, slacken and tighten.