horn

Concise Oxford English Dictionary © 2008 Oxford University Press:
horn/hɔːn/

▶noun

• 1 an outgrowth of bone encased in hardened skin, often curved and pointed, found in pairs on the heads of cattle, sheep, goats, etc.

  ■ a hardened woolly outgrowth occurring singly or one behind another on the snout of a rhinoceros.

  ■ a horn-like projection on the head of another animal, e.g. a snail's tentacle.

  ■ (horns) archaic a pair of horns as an emblem of a cuckold.

• 2 the substance of which horns are composed.

  ■ a receptacle made of horn, such as a drinking container.

• 3 a sharp promontory or mountain peak.

  ■ (the Horn) Cape Horn (in South America).

  ■ an arm or branch of a river or bay.

  ■ the extremity of the moon or other crescent.

• 4 a brass wind instrument, conical in shape or wound into a spiral.

• 5 an instrument sounding a signal.

• 6 Brit. vulgar slang an erect penis.

▶verb

• 1 butt or gore with the horns.

• 2 (horn in) informal interfere.

– phrases
blow (or toot) one's own horn N. Amer. informal boast about oneself or one's achievements.
draw (or pull) in one's horns become less assertive or ambitious.
on the horn N. Amer. informal on the telephone.
on the horns of a dilemma faced with a decision involving equally unfavourable alternatives.

– derivatives
horned adjective,
hornist noun,
hornless adjective,
horn-like adjective.

– origin OE, of Gmc origin.