‖n. pl. [ L. lapillus a little stone, dim. of lapis stone. ] (Min.) Volcanic ashes, consisting of small, angular, stony fragments or particles. [ 1913 Webster ]

n. plural of bacillus; usually designating aerobic rod-shaped spore-producing bacteria; they often occur in chainlike formations.
Syn. -- bacillus [ WordNet 1.5 ]

a. [ L. bacillum little staff + -form. ] Rod-shaped. [ 1913 Webster ]