Freshwater char (4)
I believe the answer is:
burn
I believe this is a double definition.
'freshwater' is the first definition.
(a burn is a type of stream)
'char' is the second definition.
(thesaurus)
(Other definitions for burn that I've seen before include "Incinerate" , "Copy (a CD)" , "Injury from flame" , "Small stream in Scotland" , "Scottish brook" .)