Unmarried, not having pound to burn (5)
I believe the answer is:
singe
'burn' is the definition.
(singe is a kind of burn)
'unmarried not having pound' is the wordplay.
'unmarried' becomes 'single-' (similar in meaning).
'not having' is a deletion indicator.
'pound' becomes 'L' (abbreviation e.g. Lsd - pounds, shillings, pence).
'single' with 'l' taken out is 'SINGE'.
'to' is the link.
(Other definitions for singe that I've seen before include "Result of burning" , "Burn slightly on surface" , "Char, scorch" , "Earnest entreaty" , "Scorch lightly" .)