if

conj

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?”

   “If you prefer, I can come tomorrow instead.”

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

   “I'll come only if you will do the driving.”

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".”

   “She could have used my car if the battery wasn't flat.”

4. (excessive, usually)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!”

   ““Wait a minute!” said the girl: “I wouldn’t hurry by, if it was you that was coming out to be hung, the next time eight o’clock struck, Bill. I’d walk round and round the place till I dropped, if the snow was on the ground, and I hadn’t a shawl to cover me.””

   “If it’s the last thing I do / If it takes me from Tubilo to Timbuktu / If it’s the last thing I do / I’m gonna dodge every road block, speed trap, county cop / To get my hands on you / If it’s the last thing I do.”

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.”

   “Both Spear & Davis were indicted in the witchhunt surrounding the sensational (if nonexistent) "Revere sex ring."”

8. (proscribed, sometimes)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, / […] ””

   “It is doubtful if the Victorian Londoner needed any warning, for the artful mobsmen, toolers, whizzers and dippers, together with their stickman accomplices, were everywhere in the crowds, in the underground, on railway trains […]”

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. (rare)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.”

    “If the Russians out-produced the Japanese in individual units, the Japanese out-produced the USSR in terms of technological quality.”

    “If the Americans knew how they wanted to use strategic air power but not what to attack, the British had a huge number of plans about what to attack but almost no means to adequately deliver the necessary blow.”

    “If the Poles resisted imperial rule, the Ukrainians threatened the unity of the “reunified” Catherinian empire by claiming an identity distinct from the Russian.”

noun

1. (informal)An uncertainty, possibility, condition, doubt etc.

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

   “1709, Susannah Centlivre, The Busy Body, Act III, in John Bell (ed.), British Theater, J. Bell (1791), page 59, Sir Fran. Nay, but Chargy, if——— ¶ Miran. Nay, Gardy, no Ifs.——Have I refus'd three northern lords, two British peers, and half a score knights, to have put in your Ifs?”

   “Well might Bergman add, (in his Sciographia,), “if the compariſon that has been made, &c. be juſt.” The preſent writer makes no ifs about the matter, and has ſuperadded a little inaccuracy of his own, […]”

   “Even if they managed to strike Japan, the United States or South Korea with nuclear weapons — a big if, given that they do not have a reliable delivery system — they could not save themselves from ultimate defeat.”

2. (abbreviation, alt-of, countable, initialism, uncountable)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.”

3. (abbreviation, alt-of, countable, initialism, uncountable)Initialism of impact factor.
4. (abbreviation, alt-of, countable, initialism, uncountable)Initialism of intermediate filament.
5. (abbreviation, alt-of, countable, initialism, uncountable)Initialism of intermediate frequency.
6. (abbreviation, alt-of, countable, initialism, uncountable)Initialism of intermittent fasting.
7. (abbreviation, alt-of, countable, initialism, uncountable)Initialism of immunofluorescence.