'Unless' definitions:

Definition of 'Unless'

From: GCIDE
  • Unless \Un*less"\, conj. [Formerly, onles, onlesse, onlesse that, that is, in less, in a less case. See On, and Less.] Upon any less condition than (the fact or thing stated in the sentence or clause which follows); if not; supposing that not; if it be not; were it not that; except; as, we shall fail unless we are industrious. [1913 Webster]
  • Note: By the omission of the verb in the dependent clause, unless was frequently used prepositionally, -- a construction common in Shakespeare and still employed colloquially. [1913 Webster]
  • Here nothing breeds unless the nightly owl. --Shak. [1913 Webster]

Synonyms of 'unless'

From: Moby Thesaurus