Retreat for a chap about fifty (6)
I believe the answer is:
alcove
'retreat' is the definition.
(thesaurus)
'a chap about fifty' is the wordplay.
'chap' becomes 'cove' (British slang term).
'about' says to put letters next to each other.
'fifty' becomes 'l' (Roman numeral).
'cove' put after 'l' is 'lcove'.
'a'+'lcove'='ALCOVE'
'for' acts as a link.
(Other definitions for alcove that I've seen before include "Niche - retreat" , "Small recess in a larger room" , "Small opening - a clove (anag)" , "Recessed part of a room" , "nook" .)