Heard to foretell implement (5)
I believe the answer is:
auger
'implement' is the definition.
(auger is a kind of implement)
'heard to foretell' is the wordplay.
'heard' shows a homophone (sound like).
'to foretell' becomes 'augur' (auguring is a kind of foretelling).
'augur' is a homophone of 'AUGER'.
(Other definitions for auger that I've seen before include "Tool with spiral point for boring" , "A drilling tool" , "something that's boring" , "Boring instrument" , "Boring-tool" .)