Scorch most of map (4)
I believe the answer is:
char
'scorch' is the definition.
(I know that scorch can be written as char)
'most of map' is the wordplay.
'most of' means to remove the last letter.
'map' becomes 'chart' (synonyms).
'chart' with its last letter removed is 'CHAR'.
(Other definitions for char that I've seen before include "Kind of small trout - burn it black" , "Scorch - fish - cleaning lady" , "Make black by burning, or a small trout" , "way to make carbon" , "Overcook - fish - daily" .)