The thing about husband, a source of irritation (4)
I believe the answer is:
itch
'a source of irritation' is the definition.
(I've seen this before)
'the thing about husband' is the wordplay.
'the thing' becomes 'it'.
'about' becomes 'c' (abbreviation for 'circa'**).
'husband' becomes 'h'.
'it'+'c'+'h'='ITCH'
(Other definitions for itch that I've seen before include "Constant desire" , "burn" , "longing for something" , "Strong desire to do something" , "Yearn" .)