whistling vs signalling

whistling and signalling both are nouns.

Word	Noun	Adjective	Verb	Adverb
whistling	Yes	No	No	No
signalling	Yes	No	No	No

As nouns, signalling is a hypernym of whistling; that is, signalling is a word with a broader meaning than whistling:

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

Other hypernyms of whistling include sign, signal, signaling.

whistling (noun)	signalling (noun)
the act of whistling a tune	any nonverbal action or gesture that encodes a message
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