Crossword Genius

Staunch pal's defeat on board (9)

Ross

I believe the answer is:

checkmate

I'm a little stuck... Click here to teach me more about this clue!

'defeat on board' is the definition.
(I've seen this before)

'staunch pal's' is the wordplay.
'staunch' becomes 'check' (I can't justify this - if you can you should believe this answer much more).
'pal' becomes 'mate' (I've seen this before).
'check'+'mate'='CHECKMATE'

Can you help me to learn more?

(Other definitions for checkmate that I've seen before include "Winning call on board" , "Inescapable attack in chess" , "Chess game ending" , "game's up now" , "Where the king can't move" .)

I've seen this clue in The Telegraph.
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