1. [n]  (Greek mythology) one of the heroes who sailed with Jason on the Argo in search of the Golden Fleece
2. [n]  someone engaged in a dangerous but potentially rewarding adventure

ARGONAUT is a 8 letter word that starts with A.

1. \Ar"go*naut\, n. [L. Argonauta, Gr. ?; ? + ? sailor, ?
   ship. See {Argo}.]
   1. Any one of the legendary Greek heroes who sailed with
      Jason, in the Argo, in quest of the Golden Fleece.
   2. (Zo["o]l.) A cephalopod of the genus Argonauta.
   

2. \Ar"go*naut\, n.
   One of those who went to California in search of gold shortly
   after it was discovered there in 1848. [U. S.] --Bret Harte.
         The ``Argonauts of '49'' were a strong, self-reliant,
         generous body of men.                    --D. S.
                                                  Jordan.