tapping vs rat-a-tat

tapping and rat-a-tat both are nouns.

Word	Noun	Adjective	Verb	Adverb
tapping	Yes	No	No	No
rat-a-tat	Yes	No	No	No

As nouns, rat-a-tat is a hyponym of tapping; that is, rat-a-tat is a word with a more specific, narrower meaning than tapping:

tapping: the sound of light blow or knock
rat-a-tat: a series of short sharp taps (as made by strokes on a drum or knocks on a door)

Other hyponyms of tapping include rat-a-tat-tat, rat-tat.

tapping (noun)	rat-a-tat (noun)
the sound of light blow or knock	a series of short sharp taps (as made by strokes on a drum or knocks on a door)