Paddleboat's left side or its terminus (4)
I believe the answer is:
port
This clue is a double definition.
'paddleboat's left side' is the first definition.
(port can mean the left side on a boat)
'terminus' is the second definition.
(thesaurus)
'or its' acts as a link.
(Other definitions for port that I've seen before include "After-dinner wine" , "Left, opening, wine" , "Isle in Dorset" , "Sweet red wine for after dinner" , "Harbour; drink; opening" .)