Lady’s husband about to retire (3)
I believe the answer is:
her
'lady's' is the definition.
(her refers to a woman)
'husband about to retire' is the wordplay.
'husband' becomes 'h' (abbreviation).
'about' becomes 're' (regarding).
'to retire' says the letters should be written backwards (retire can mean to go back).
're' back-to-front is 'er'.
'h'+'er'='HER'
(Other definitions for her that I've seen before include "In the Midlands she" , "That lady" , "That lady's" , "Pronoun used of ship" , "Belonging to the woman" .)