it/that won't do(redirected from it won't do)
it/that (just) won’t ˈdo,
it/that will never ˈdo(especially British English) used to say that a situation is not satisfactory and should be changed or improved: He’s spending every afternoon in the park with his friends instead of going to school, and that just won’t do! ♢ I feel very upset but it would never do to show it.
See also: that