Firm’s short stockings (5)
I believe the answer is:
tight
'firm's' is the definition.
(synonyms)
'short stockings' is the wordplay.
'short' means to remove the last letter.
'stockings' becomes 'tights' (tights can mean stockings).
'tights' with its last letter taken off is 'TIGHT'.
(Other definitions for tight that I've seen before include "Trim" , "South American nation" , "Mean; firmly fixed" , "Secretive, drunk (colloq.)" , "Firmly fastened; drunk" .)