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.
2. any substance that inhibits growth of microorganisms; this is contrasted to a germicide, which kills them outright. The category antiseptics is also not considered to include antibiotics, which are usually taken internally, although it does include disinfectants.