Husband, base, simple and unfeeling (9)
I believe the answer is:
heartless
'unfeeling' is the definition.
(heartless can mean lacking feeling)
'husband base simple' is the wordplay.
'husband' becomes 'h' (abbreviation).
'base' becomes 'e' (Euler's number - base of natural logarithms).
'simple' becomes 'artless' (similar in meaning).
'h'+'e'+'artless'='HEARTLESS'
'and' acts as a link.
(Other definitions for heartless that I've seen before include "insensitive" , "Scrooge was" , "Callous" , "Cruel and unfeeling" , "Cold-blooded" .)