Source : Webster's Revised Unabridged Dictionary (1913)

Bacillus \Ba*cil"lus\, n.; pl. {Bacilli}. [NL., for L. bacillum.
   See {Bacillarle}.] (Biol.)
   A variety of bacterium; a microscopic, rod-shaped vegetable
   organism.

Source : WordNet®

Bacilli
     n : aerobic rod-shaped spore-producing bacterium; often
         occurring in chainlike formations; found primarily in
         soil [syn: {Bacillus}, {B}]