Substantial gap (4)
I believe the answer is:
gulf
(Other definitions for gulf that I've seen before include "Deep wide chasm" , "Sound" , "Chasm, large gap" , "Large deep bay" , "Rift" .)
I believe the answer is:
gulf
(Other definitions for gulf that I've seen before include "Deep wide chasm" , "Sound" , "Chasm, large gap" , "Large deep bay" , "Rift" .)