Steamship round river doesn't leave (5)
I believe the answer is:
stays
'doesn't leave' is the definition.
(I've seen this in another clue)
'steamship round river' is the wordplay.
'steamship' becomes 'ss' (nautical abbreviation).
'round' indicates putting letters inside.
'river' becomes 'tay' (Scottish river).
'ss' enclosing 'tay' is 'STAYS'.
(Other definitions for stays that I've seen before include "Remains; corset" , "Remains; support wires" , "Corsets" , "Old-fashioned corset" , "Guys; remains" .)