If synonyms such as doubt, allowing (that), condition, and constraint. If is a conjunction, and its antonyms are unless, certainly, and definitely. Additionally, here are 33 synonyms, related words, and verbs for if.
allowing (that), allowing that, as long as, assuming (that), contingent on, given that, if and only if, in the event that, on condition that, on the assumption that, presuming (that), provided (that), providing (that), supposing (that), and with/on the understanding that.
condition, constraint, doubt, hesitation, lack of certainty, modification, precondition, prerequisite, provision, proviso, requirement, restriction, specification, stipulation, supposition, uncertainty, and vagueness.