if

conj

Etymology: From Middle English if, yif, yef, from Old English ġif (“if”), from Proto-West Germanic *jabu, *jabē, from Proto-Germanic *jabai (“when, if”). Cognate with Scots gif (“if, whether”), Saterland Frisian af, of (“if, whether”), West Frisian oft (“whether”), Dutch of (“or, whether, but”), Middle Low German ef, if, af, of ("if; whether"; > German Low German of), German ob (“if, whether”), Icelandic ef (“if”).

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

   “If crossing the road, make sure you look both ways.”

   “If I give you the money would/will you buy it for me?”

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

   “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.”

   “"You would be healthier if you would give up smoking" "Well, if I were rich, I'd go to one of those hypnosis therapies to quit".”

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

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

   “You're finishing your chowder if you sit there all afernoon!”

5. 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.”

   “O what of Gods then boots it to be borne, / If old Aveugles ſonnes ſo euill heare?”

6. When; whenever; every time that.

   “If you heat water to 100° C, it boils.”

   “If it rains, it pours.”

7. Although; used to introduce a concession; may..but.

   “He was a great friend, if a little stingy at the bar.”

   “She won her team's admiration, if not the award, for her performance.”

8. Whether; used to introduce a noun clause, an indirect question, that functions as the direct object of certain verbs.

   “I don't know if I want to go or not.”

   “Quoth Matthew, “ […] / She doubts if two and two make four, / […] ””

9. Introducing a relevance conditional; in case.

   “I have leftover cake if you want some.”

   “If you want to go home, I have the car keys.”

10. While; used to introduce a contrast.

    “If his Russian was music, his English was murder.”

    “If the outcome of the land war on the Eastern Front is usually seen as decisive, historical views on the importance of the air war are mixed.”

noun

1. Initialism of interactive fiction.

   “The “Zarfian Cruelty Scale” rates games as Merciful, Polite, Tough, Nasty, or Cruel. The scale describes how works of IF become unwinnable, especially how and when the interactor (here a player, and one trying to win) learns this.”

2. Initialism of impact factor.
3. Initialism of intermediate filament.
4. Initialism of intermediate frequency.
5. Initialism of intermittent fasting.
6. Initialism of immunofluorescence.