antibiotic UK /ˌæn.ti.baɪˈɒt.ɪk/US /ˌæn.taɪ.baɪˈɑ.tɪk/adjective 2noun 1forms 3 adjective2 •Of or relating to antibiotics. •(no longer used) Of or relating to the theory that extraterrestrial life does not exist. noun1 •Any substance that can destroy or inhibit the growth of bacteria and similar microorganisms, generally transported by the lymphatic system.We selected colistimethate sodium (CMS) as our antibiotic of choice. — 2015 formsantibiotics · more antibiotic · most antibiotic