common chord vs triad

common chord and triad both are nouns.

Word	Noun	Adjective	Verb	Adverb
common chord	Yes	No	No	No
triad	Yes	No	No	No

As nouns, common chord and triad are synonyms defined as:

common chord and triad: a three-note major or minor chord; a note and its third and fifth tones

common chord (noun)	triad (noun)
a three-note major or minor chord; a note and its third and fifth tones	a three-note major or minor chord; a note and its third and fifth tones
	three people considered as a unit
	a set of three similar things considered as a unit
	the cardinal number that is the sum of one and one and one