One on board red ship by isle (8)
I believe the answer is:
chessman
'one on board' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'red ship by isle' is the wordplay.
'red' becomes 'Che' (as in Che Guevara, a communist or 'red').
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'by' says to put letters next to each other.
'isle' becomes 'man' (the Isle of Man is an example).
'che'+'ss'+'man'='CHESSMAN'
Can you help me to learn more?
(Other definitions for chessman that I've seen before include "Playing piece" , "queen, perhaps" , "Eg, bishop or rook" , "that's played on board" , "Eg, bishop, knight" .)