Coat and line the groove (6)
I believe the answer is:
furrow
'the groove' is the definition.
(thesaurus)
'coat and line' is the wordplay.
'coat' becomes 'fur' (fur is a kind of coat).
'and' is a charade indicator (letters next to each other).
'line' becomes 'row' (row is a kind of line**).
'fur'+'row'='FURROW'
(Other definitions for furrow that I've seen before include "Channel; wrinkle" , "It's groovy!" , "A long groove or deep wrinkle" , "Groove made by plough, or wrinkle in forehead" , "Shallow trench made by a plough" .)