Keeps a ship going round a river (5)
I believe the answer is:
stays
'keeps' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Maybe you can see an association between them that I can't see?
'a ship going round a river' is the wordplay.
'a ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'going round' indicates putting letters inside (some letters go around others).
'a river' becomes 'tay' (River Tay).
'ss' enclosing 'tay' is 'STAYS'.
Can you help me to learn more?
(Other definitions for stays that I've seen before include "Boards, lodges" , "for a slimmer figure" , "Remains (in place)" , "Puts up with" , "Supports" .)