A rug lad unravelled bit by bit (7)
I believe the answer is:
gradual
'bit by bit' is the definition.
(I've seen this before)
'a rug lad unravelled' is the wordplay.
'unravelled' is an anagram indicator.
'a'+'rug'+'lad'='aruglad'
'aruglad' with letters rearranged gives 'GRADUAL'.
(Other definitions for gradual that I've seen before include "Developing in small steps" , "Proceeding in small stages" , "Happening slowly and by degrees" , "Little by little, not too fast" , "Progressing slowly" .)