Scorch grass close to furnace (5)
I believe the answer is:
singe
'scorch' is the definition.
('singe' can be a synonym of 'scorch')
'grass close to furnace' is the wordplay.
'grass' becomes 'sing' (I've seen this in other clues).
'close to' indicates one should take the final letters (the close/ending of).
The final letter of 'furnace' is 'e'.
'sing'+'e'='SINGE'
(Other definitions for singe that I've seen before include "slight burn" , "Scorch lightly" , "Result of match accident" , "Char, burn slightly" , "Burn; ignes (anag.)" .)