Negligible little chap (7)
I believe the answer is:
minimal
'negligible' is the definition.
(similar in meaning)
'little chap' is the wordplay.
'little' becomes 'mini'.
'chap' becomes 'mal' ().
'mini'+'mal'='MINIMAL'
(Other definitions for minimal that I've seen before include "Of a smallest amount" , "Very small, the least possible (7)" , "Least possible; negligible" , "Of the least possible size" , "Very little" .)