AGAR-AGAR is a 9 letter word that starts with A.

1. \A`gar-a"gar\, n. [Ceylonese local name.]
   A fucus or seaweed much used in the East for soups and
   jellies; Ceylon moss ({Gracilaria lichenoides}).
   
   

2. \A`gar-a"gar\, n.
   A gelatinlike substance, or a solution of it, prepared from
   certain seaweeds containing gelose, and used in the
   artificial cultivation of bacteria; -- often called {agar},
   by abbreviation.