Son to accept bet (5)
I believe the answer is:
stake
'bet' is the definition.
(staking is a kind of betting)
'son to accept' is the wordplay.
'son' becomes 's'.
'to accept' becomes 'take' (taking is a kind of accepting).
's'+'take'='STAKE'
(Other definitions for stake that I've seen before include "Post; money for bet" , "Keats (anag.)" , "Post; money wagered" , "Investment" , "Wooden post; ante" .)