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.
Definition of antibiotic. : a substance produced by or a semisynthetic (see semisynthetic 1) substance derived from a microorganism and able in dilute solution to inhibit or kill another microorganism The doctor prescribed an antibiotic to treat the infection.