I. noun a medicine (such as penicillin or its derivatives) that inhibits the growth of or destroys microorganisms. • course of antibiotics.
• [ mass noun]
an injection of antibiotic.
II. adjective relating to antibiotics. • a prolonged course of antibiotic therapy.
– origin mid 19th cent. (in the sense ‘doubting the possibility of life in a particular environment’): from anti- + Greek biōtikos ‘fit for life’ (from bios ‘life’).