Deep wide chasm (4)
I believe the answer is:
gulf
'deep wide chasm' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gulf that I've seen before include "Deep inlet of sea; chasm" , "Unbridgeable disparity" , "Deep wide chasm" , "Larger or more indented bay" , "Wide gap; arm of sea" .)