unless
conj.conj. except if something else happens. You use it to show that a situation will only change if a specific condition is met.
conj. except on the condition that; used to introduce a case in which a preceding statement is not true or valid.
I will go for a walk unless it rains.
The store will not accept any returns unless you provide the original receipt as proof of purchase.
The board of directors will likely approve the merger unless the final audit reveals significant undisclosed debts that threaten the company's long-term stability.
From Middle English unlesse, earlier on lesse (modern on + less), from (not) on lesse (than) (“(not) on a less compelling condition (than)”). The quality of negation in the word and the lack of stress changed on to un-.
Introduces a subordinate clause; often used as an alternative to 'if... not'.
I will stay home unless it will rain.I will stay home unless it rains.In clauses starting with 'unless' that refer to the future, use the present simple tense instead of 'will'.