Port on Adriatic's eastern side? Split (5)
I believe the answer is:
cleft
'side? split' is the definition.
'cleft' can be an answer for 'split' (I've seen this before). I'm unsure of the 'side?' bit.
'port on adriatic's eastern' is the wordplay.
'port' becomes 'left' (port is the left side on a boat).
'on' means one lot of letters go next to another.
'adriatic's eastern' becomes 'c' (I can't justify this - if you can you should believe this answer much more).
'left' put after 'c' is 'CLEFT'.
Can you help me to learn more?
(Other definitions for cleft that I've seen before include "Narrow gap" , "rent" , "Chin split" , "Split in the palate" , "Space" .)