whistle vs signal

whistle and signal both are nouns.

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

As nouns, signal is a hypernym of whistle; that is, signal is a word with a broader meaning than whistle:

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

Other hypernyms of whistle include sign, signaling, signalling.

As verbs, signal is a hypernym of whistle; that is, signal is a word with a broader meaning than whistle:

Other hypernyms of whistle include sign, signalise, signalize.

whistle (noun)	signal (noun)
an inexpensive fipple flute	any nonverbal action or gesture that encodes a message
acoustic device that forces air or steam against an edge or into a cavity and so produces a loud shrill sound	any incitement to action
a small wind instrument that produces a whistling sound by blowing into it	an electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes
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

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

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