River-snakes provide filing tools (5)
I believe the answer is:
rasps
'filing tools' is the definition.
(I've seen this in another clue)
'river-snakes' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'snakes' becomes 'asps' (asp is a kind of snake).
'r'+'asps'='RASPS'
'provide' acts as a link.
(Other definitions for rasps that I've seen before include "Jars" , "speaks hoarsely" , "Grates harshly" , "fruit briefly" , "Coarse files" .)