Conformity of a triad, say (6)
I believe the answer is:
accord
'conformity' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for accord that I've seen before include "Consent or agreement" , "Harmony and fellowship" , "Harmonize" , "Unanimity" , "Harmony, concurrence" .)