With nag, husband's left more disagreeable (5)
I believe the answer is:
worse
'more disagreeable' is the definition.
(worse means more disagreeable or less good)
'with nag husband's left' is the wordplay.
'with' becomes 'w' (abbreviation).
'nag' becomes 'horse' (a nag is an old horse).
'husband' becomes 'h' (abbreviation).
'left' indicates named letters should be taken away (some letters have left).
'horse' with 'h' taken away is 'orse'.
'w'+'orse'='WORSE'
(Other definitions for worse that I've seen before include "More serious" , "More awful or unwell" , "more unpleasant" , "Less favourable" , "less moral?" .)