1.  warn(v = verb.communication) - notify of danger, potential harm, or risk; "The director warned him that he might be fired"; "The doctor warned me about the dangers of smoking"
is one way to inform
Derived forms noun warner₂, noun warning₁
Sample sentences: Somebody ----s; Somebody ----s somebody; Something ----s somebody; Somebody ----s somebody of something; Somebody ----s that CLAUSE

2.  warn(v = verb.communication) admonish, discourage, monish - admonish or counsel in terms of someone's behavior; "I warned him not to go too far"; "I warn you against false assumptions"; "She warned him to be quiet"
is one way to advise, counsel, rede
Derived form noun warning₂
Sample sentences: Sam cannot warn Sue

3.  warn(v = verb.communication) - ask to go away; "The old man warned the children off his property"
is one way to enjoin, order, say, tell
Sample sentences: Somebody ----s somebody PP

4.  warn(v = verb.communication) - notify, usually in advance; "I warned you that I would ask some difficult questions"
is one way to inform
Derived form noun warner₂
Sample sentences: Somebody ----s somebody

   To refuse. Chaucer. [1913 Webster]

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. Dryden. [1913 Webster]
"Cornelius the centurion . . . was warned from God by an holy angel to send for thee." [1913 Webster]
"Who is it that hath warned us to the walls?" [1913 Webster]

2.  To give notice to, of approaching or probable danger or evil; to caution against anything that may prove injurious. Dryden. [1913 Webster]

3.  To ward off. Spenser. [1913 Webster]

warn, v.tr.
1 (also absol.) a (often foll. by of, or that + clause, or to + infin.) inform of danger, unknown circumstances, etc. (warned them of the danger; warned her that she was being watched; warned him to expect a visit). b (often foll. by against) inform (a person etc.) about a specific danger, hostile person, etc. (warned her against trusting him).
2 (usu. with neg.) admonish; tell forcefully (has been warned not to go).
3 give (a person) cautionary notice regarding conduct etc. (shall not warn you again).

Idiom:
warn off
1 tell (a person) to keep away (from).
2 prohibit from attending races, esp. at a specified course.

Derivative:
warner n.

Etymology:
OE war(e)nian, wearnian ult. f. Gmc: cf. WARE(3)

VB  dissuade, dehort, cry out against, remonstrate, expostulate, warn, contraindicate, disincline, indispose, shake, stagger, dispirit, discourage, dishearten, deter, repress, hold back, keep back, render averse, repel, turn aside, wean from, act as a drag, throw cold water on, damp, cool, chill, blunt, calm, quiet, quench, deprecate, disenchant, disillusion, deflate, take down a peg, pop one's balloon, prick one's balloon, burst one's bubble, disabuse (correction).

VB  warn, caution, forewarn, prewarn, admonish, premonish, give notice, give warning, dehort, menace, put on one's guard, sound the alarm, croak, beware, ware, take warning, take heed at one's peril, keep watch and ward.

VB  give the alarm, raise the alarm, sound the alarm, turn in the alarm, beat the alarm, give an alarm, raise an alarm, sound an alarm, turn in an alarm, beat an alarm, alarm, warn, ring the tocsin, battre la generale, cry wolf.