Traitorous motive in board (11)
I believe the answer is:
treasonable
'traitorous' is the definition.
(synonyms)
'motive in board' is the wordplay.
'motive' becomes 'reason' (reason is a kind of motive).
'in' means one lot of letters goes inside another.
'board' becomes 'table' (both can mean food).
'reason' going inside 'table' is 'TREASONABLE'.
(Other definitions for treasonable that I've seen before include "(Of offence) relating to betrayal of one's country" , "giving people away" , "in relation to crime against state" , "aiming to put down the boss?" , "Subversive" .)