Unless

Unless - (Webster's 1828 Dictionary)

UNLESS', conj.

Except; that is, remove or dismiss the fact or thing stated in the sentence or clause which follows. ""We cannot thrive unless we are industrious and frugal."" the sense will be more obvious with the clauses of the sentence inverted. Unless, [remove this fact, suppose it not to exist,] we are industrious and frugal, we cannot thrive. Unless then answers for a negation. If we are not industrious, we cannot thrive.