Woodwind lessons somewhat in decline (7)
I believe the answer is:
dwindle
'decline' is the definition.
(I've seen this before)
'woodwind lessons somewhat in' is the wordplay.
'in' indicates the answer is hidden within the clue.
'DWINDLE' is hidden in the letters of 'woodwind lessons somewhat'.
(Other definitions for dwindle that I've seen before include "Degenerate" , "Grow less - waste away" , "Flag" , "Die away" , "become weaker" .)