Deep gulf
I think it could be either:
'deep gulf' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for abyss that I've seen before include "crevasse" , "Deep gulf" , "Very deep gorge" , "Deep hole, seems bottomless" , "Primal chaos" .)
'deep gulf' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for abysm that I've seen before include "Deep hole" , "Gorge" , "Deep cavity (arch)" , "Hell" , "Bottomless pit" .)