Hide line crease (6)
I believe the answer is:
furrow
'crease' is the definition.
(I know that crease can be written as furrow)
'hide line' is the wordplay.
'hide' becomes 'fur' (animal fur).
'line' becomes 'row' (a row or line of things).
'fur'+'row'='FURROW'
(Other definitions for furrow that I've seen before include "Long groove in ground or wrinkle in forehead" , "Shallow trench made by a plough" , "Ploughing mark" , "It's groovy!" , "Wrinkle (brow)" .)