Home › Words › P › polymyxinpolymyxinpolymyxin means any of several toxic antibiotics, derived from the soil bacterium Bacillus polymyxa, used to treat infections by gram-negative bacteria.Among words judged in Lexicurio's Arena, polymyxin ranks #36,069 of 42,752 for Qualifying.EtymologyFrom translingual polymyxa + -in, from Bacillus polymyxa, from which the antibiotic was isolated.nounAny of several toxic antibiotics, derived from the soil bacterium Bacillus polymyxa, used to treat infections by gram-negative bacteriaDefinitions & examples from Wiktionary (CC BY-SA 3.0).