Unmarried son leaves fireside (5)
I believe the answer is:
ingle
'fireside' is the definition.
(thesaurus)
'unmarried son leaves' is the wordplay.
'unmarried' becomes 'single' ('single' can be similar in meaning to 'unmarried').
'son' becomes 's'.
'leaves' suggests deleting specific letters.
'single' with 's' taken out is 'INGLE'.
(Other definitions for ingle that I've seen before include "Fireplace (mainly dialect)" , "A fireside nook - get leg in" , "Dizziness from imbalance" , "Corner, nook" , "Catamite" .)