At his core, smug lyricist produces harmony (5)
I believe the answer is:
music
'harmony' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for music that I've seen before include "Organised sound" , "(Pleasant) sequence of sounds" , "'If ... be the food of love, play on'(Twelfth Night)" , "Aural entertainment" , "'''If ... be the food of love, play on'' (Twelfth Night) (5)'" .)