Horsemen on board? (7)
I believe the answer is:
knights
'horsemen on board?' is the definition.
The definition and answer can be both people as well as being plural nouns.
Perhaps you can see a link between them that I can't see?
This is all the clue.
Can you help me to learn more?
(Other definitions for knights that I've seen before include "Also 3 down" , "Chess pieces" , "Chessmen shaped as head of horse" , "Honoured men" .)