if

conjunction

1. Supposing that, assuming that, in the circumstances that; suppositive used to introduce a condition that may be (or prove to be) either true or false.

   “I'll do it next week if I have time.”

2. A keyword that invokes conditional processing: in the event that a given condition is true, execute the given statement(s) (otherwise execute other statements).

   “if A then B else C”

3. Supposing that; used with past or past perfect subjunctive to indicate a counterfactual or hypothetical condition.

   “If she hadn't told me, I wouldn't know.”

4. Even if; even in the circumstances that.

   “I wouldn't marry you if you were the last man on earth.”

noun

1. An uncertainty, possibility, condition, doubt etc.

   “The board can't approve this project; there are too many ifs.”