grass bacillus grass·ba·cil·lus uncommon noun 1. a species of Bacillus found in soil and decomposing organic matter; some strains produce antibiotics SynonymsBacillus subtilisBacillus globigiigrass bacillushay bacillus Related words Broader terms Bacillus WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.
