signal vs whistle

signal and whistle both are nouns.

Word	Noun	Adjective	Verb	Adverb
signal	Yes	Yes	Yes	No
whistle	Yes	No	Yes	No

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

signal: any nonverbal action or gesture that encodes a message
whistle: the act of signalling (e.g., summoning) by whistling or blowing a whistle

As verbs, whistle is a hyponym of signal; that is, whistle is a word with a more specific, narrower meaning than signal:

Other hyponyms of signal include wigwag, semaphore, heliograph, flag.

signal (noun)	whistle (noun)
any nonverbal action or gesture that encodes a message	an inexpensive fipple flute
any incitement to action	acoustic device that forces air or steam against an edge or into a cavity and so produces a loud shrill sound
an electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes	a small wind instrument that produces a whistling sound by blowing into it
	the act of signalling (e.g., summoning) by whistling or blowing a whistle
	the sound made by something moving rapidly or by steam coming out of a small aperture

signal (adjective)	whistle (adjective)
notably out of the ordinary

signal (verb)	whistle (verb)
communicate silently and non-verbally by signals or signs	utter or express by whistling
be a signal for or a symptom of	make a whining, ringing, or whistling sound
	give a signal by whistling
	move with, or as with, a whistling sound
	move, send, or bring as if by whistling
	make whistling sounds