iff

Conjunction

if and only if

1. Is equivalent to; implies and is implied by; is true and false in the same cases as.
   • A rectangle is a square if and only if all four of its sides have the same length.
2. (broadly, informal) Synonym of if (with added intensity)
   • I'll let you go to the concert if and only if you clean your room.

   Synonyms:

   if

Conjunction

if

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.
   1. 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
2. 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.
   1. (excessive, usually) Even if; even in the circumstances that.
      • I wouldn't marry you if you were the last man on earth.
3. Considering the fact that; given that; introducing a condition that is known to be true.
   • The drain's blocked — and if the drain's blocked, the water won't flow.
4. When; whenever; every time that.
   • If you heat water to 100° C, it boils.

See all 11 meanings of if