Definition of illegal. : not according to or authorized by law : unlawful, illicit; also : not sanctioned by official rules (as of a game)
antibiotic. n. 1. (Pharmacology) any of various chemical substances, such as penicillin, streptomycin, chloramphenicol, and tetracycline, produced by various microorganisms, esp fungi, or made synthetically and capable of destroying or inhibiting the growth of microorganisms, esp bacteria. adj.
Antibiotics or antibacterials are a type of antimicrobial used in the treatment and prevention of bacterial infection.ntibiotics are not effective against viruses such as the common cold or influenza, and may be harmful when taken inappropriately. In 1929, Alexander Fleming identified penicillin, the first chemical compound with antibiotic properties.