Cleft, crack (7)
I believe the answer is:
crevice
I believe this clue is a double definition.
'cleft' is the first definition.
(I know that cleft can be written as crevice)
'crack' is the second definition.
(I know that crack can be written as crevice)
(Other definitions for crevice that I've seen before include "Crack or fissure." , "Split" , "Cleft, fissure" , "Narrow rock fissure" , "Narrow crack" .)