Drifting around chasm (4)
I believe the answer is:
rift
'chasm' is the definition.
(I've seen this in another clue)
'drifting around' is the wordplay.
'around' indicates a hidden word.
'RIFT' is hidden within 'drifting'.
(Other definitions for rift that I've seen before include "cleavage" , "Lack of harmony" , "Breach or quarrel" , "Breach or crevasse" , "Cleft or fissure" .)