On a vehicle such as a car, the horn is the device that makes a loud noise as a signal or warning. He sounded the car horn. 2. countable noun [usually plural] The horns of an animal such as a cow or deer are the hard pointed things that grow from its head.

Slang. a telephone or radiotelephone: I've been on the horn all morning. the high protuberant part at the front and top of certain saddles; a pommel, especially a high one.

Horns provide a diversity of important functions for the animals bearing them, such as defense from predators, tools in fighting other members of the species for territory or mating, feeding, courtship displays, and cooling.

Ig meets Lee by the docks and pulls off Merrin's necklace. He realizes Lee was unable to see the horns because he was wearing the necklace. Exposed to the horns, Lee falls under their influence and admits to killing Merrin.