Spare money cut by husband (4)
I believe the answer is:
thin
'spare' is the definition.
(similar in meaning)
'money cut by husband' is the wordplay.
'money' becomes 'tin' (old-fashioned slang term for money).
'cut by' indicates putting letters inside (some letters cut into others).
'husband' becomes 'h'.
'tin' enclosing 'h' is 'THIN'.
(Other definitions for thin that I've seen before include "Insubstantial" , "Slender, slight" , "Having little width" , "Implausible" , "Narrow, slim" .)