We don't have synonyms for ante-post yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are antepast, ante post and anteport.
(adj) :
Alternative form of antepost. [(gambling) Being a kind of bet, in horse-racing and greyhound racing, placed before the racecourse's betting market has opened, on the expectation that the price of the animal is presently more favourable than it will be when the market opens.]
(adj) :
Alternative form of antepost. [(gambling) Being a kind of bet, in horse-racing and greyhound racing, placed before the racecourse's betting market has opened, on the expectation that the price of the animal is presently more favourable than it will be when the market opens.]