Gale to develop smoothly (6)
I believe the answer is:
legato
'smoothly' is the definition.
(I've seen this before)
'gale to develop' is the wordplay.
'develop' indicates anagramming the letters.
'gale'+'to'='galeto'
'galeto' anagrammed gives 'LEGATO'.
(Other definitions for legato that I've seen before include "with smooth execution" , "running into each other" , "In music, in a smooth even manner" , "Smoothly flowing (music)" , "Smoothly (mus.)" .)