chord vs common chord

chord and common chord both are nouns.

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

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

chord: a combination of three or more notes that blend harmoniously when sounded together
common chord: a three-note major or minor chord; a note and its third and fifth tones

Other hyponyms of chord include arpeggio, sforzando, triad, seventh chord.

chord (noun)	common chord (noun)
a combination of three or more notes that blend harmoniously when sounded together	a three-note major or minor chord; a note and its third and fifth tones
a straight line connecting two points on a curve

chord (verb)	common chord (verb)
bring into consonance, harmony, or accord while making music or singing
play chords on (a stringed instrument)