Bluff bordering some deep chasm (6)
I believe the answer is:
canyon
'deep chasm' is the definition.
(I've seen this in another clue)
'bluff bordering some' is the wordplay.
'bluff' becomes 'con' (bluff can mean a trick or con).
'bordering' means one lot of letters goes inside another.
'some' becomes 'any' (similar in meaning).
'con' enclosing 'any' is 'CANYON'.
(Other definitions for canyon that I've seen before include "rift created" , "Gulch" , "A deep gorge with a river, may be Grand" , "'Deep ravine, gorge (6)'" , "Deep, steep-sided valley" .)