The Collaborative International Dictionary of English v.0.48:
Warn \Warn\, v. t. [imp. & p. p. Warned; p. pr. & vb. n.
Warning.] [OE. warnen, warnien, AS. warnian, wearnian, to
take heed, to warn; akin to AS. wearn denial, refusal, OS.
warning, wernian, to refuse, OHG. warnen, G. warnen to warn,
OFries. warna, werna, Icel. varna to refuse; and probably to
E. wary. ????.]
1. To make ware or aware; to give previous information to; to
give notice to; to notify; to admonish; hence, to notify
or summon by authority; as, to warn a town meeting; to
warn a tenant to quit a house. "Warned of the ensuing
Cornelius the centurion . . . was warned from God by
an holy angel to send for thee. --Acts x. 22.
Who is it that hath warned us to the walls? --Shak.
2. To give notice to, of approaching or probable danger or
evil; to caution against anything that may prove
injurious. "Juturna warns the Daunian chief of Lausus'
danger, urging swift relief." --Dryden.
3. To ward off. [Obs.] --Spenser.