Nothing odd about impulse -- itch -- to achieve harmony? (5)
I believe the answer is:
music
'harmony?' is the definition.
(harmony is a kind of music)
'nothing odd about impulse itch' is the wordplay.
'nothing odd about' indicates alternate letters (letters in odd-numbered positions are removed).
'impulse'+'itch'='impulseitch'
The alternate letters of 'impulseitch' are 'MUSIC'.
'to achieve' acts as a link.
(Other definitions for music that I've seen before include "melodies" , "Organised sound" , "Composed sounds" , "'My - - ' , radio quiz" , "Melodious sounds" .)