1. [n]  an agent who conducts an auction
2. [v]  sell at an auction

AUCTIONEER is a 10 letter word that starts with A.

1. \Auc`tion*eer"\, n.
   A person who sells by auction; a person whose business it is
   to dispose of goods or lands by public sale to the highest or
   best bidder.
   

2. \Auc`tion*eer"\, v. t.
   To sell by auction; to auction.
         Estates . . . advertised and auctioneered away.
                                                  --Cowper.