Split, crack (7)
I believe the answer is:
fissure
I believe this is a double definition.
'split' is the first definition.
(thesaurus)
'crack' is the second definition.
(I know that crack is a class)
(Other definitions for fissure that I've seen before include "Crevice" , "Cleft" , "Long, narrow opening" , "Split, crack" , "Long, narrow crack" .)