Some breach, a small gorge (5)
I believe the answer is:
chasm
'gorge' is the definition.
(thesaurus)
'some breach a small' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'CHASM' is hidden within 'breach a small'.
(Other definitions for chasm that I've seen before include "Abyss" , "Deep gap" , "Gorge" , "Yawning gap" , "What's split" .)