any of a group of chemically related antibiotic polypeptides produced by a soil bacillus (Bacillus brevis) and used in medicines to treat various bacterial infections, esp. of the skin and eyes
See gramicidin in American Heritage Dictionary 4
(grămˌĭ-sīdˈn)
noun
An antibiotic produced by the soil bacterium Bacillus brevis and used to treat infections caused by certain gram-positive bacteria.