Port cracked open? (5)
I believe the answer is:
split
This clue is a triple definition!
'port' is the first definition.
(I've seen this before)
'cracked' is the second definition.
(thesaurus)
'open?' is the third definition.
(thesaurus)
(Other definitions for split that I've seen before include "Break; fissure" , "Adriatic port" , "Cut, cleft" , "Left" , "shared by a couple?" .)