warning signal vs horn

warning signal and horn both are nouns.

Word	Noun	Adjective	Verb	Adverb
warning signal	Yes	No	No	No
horn	Yes	No	Yes	No

As nouns, horn is a hyponym of warning signal; that is, horn is a word with a more specific, narrower meaning than warning signal:

Other hyponyms of warning signal include torpedo, air alert, burglar alarm, fire alarm, foghorn, fogsignal, red flag, siren, alarm bell, tocsin.

warning signal (noun)	horn (noun)
an automatic signal (usually a sound) warning of danger	one of the bony outgrowths on the heads of certain ungulates
	any hard protuberance from the head of an organism that is similar to or suggestive of a horn
	a brass musical instrument consisting of a conical tube that is coiled into a spiral and played by means of valves
	a brass musical instrument with a brilliant tone; has a narrow tube and a flared bell and is played by means of valves
	an alarm device that makes a loud warning sound
	a high pommel of a Western saddle (usually metal covered with leather)
	a device on an automobile for making a warning noise
	a noisemaker (as at parties or games) that makes a loud noise when you blow through it
	a device having the shape of a horn
	a noise made by the driver of an automobile to give warning
	the material (mostly keratin) that covers the horns of ungulates and forms hooves and claws and nails

warning signal (verb)	horn (verb)
	stab or pierce with a horn or tusk