if conjunction [OE. if, gif, AS. gif; akin to OFries. ief, gef, ef, OS. ef, of, D. of, or, whether, if, G. ob whether, if, OHG. oba, ibu, Icel. ef, Goth. iba, ibai, an interrogative particle; properly a case form of a noun meaning, doubt (cf. OHG. iba doubt, condition, Icel. if, ef, ifi, efi), and therefore orig. meaning, on condition that.]

1. In case that; granting, allowing, or supposing that; – introducing a condition or supposition.

Tisiphone, that oft hast heard my prayer,
Assist, if Œdipus deserve thy care. Pope.

If thou be the Son of God, command that these stones be made bread. Matt. iv. 3.

2. Whether; – in dependent questions.

Uncertain if by augury or chance. Dryden.

She doubts if two and two make four. Prior.

As if

But if

See under As, But.

-- Webster's unabridged 1913