1) Affirmer 2) Asserter 3) Asseverator 4) Avoer 5) Avower 1) At bridge, the maker 2) Avower 3) Bridge player 4) Contractor 5) Hand 6) One going through Customs 7) One possibly seeking a slam 8) Trump namer 
• (n.) One who makes known or proclaims; that which exhibits.
De·clar'er noun One who makes known or proclaims; that which exhibits. Udall. 
noun the bridge player in contract bridge who wins the bidding and can declare which suit is to be trumps
The player who is the first to bid the suit (or no trump) of the final contract.
a person or thing that declares. · the player who plays the contract; dummy's partner.
By winning the bidding, you become the declarer. You get to pick up and then discard the kitty and declare the trump suit. You could also call a card and declare a Durch or Untendurch game when using certain custom rules. As declarer, you must reach your bid value by the end of the round. Otherwise, you overbid and face the penalty for losing.