1.NounA synthetic fluoroquinolone antibiotic structurally related to nalidixic acid, which is used topically to treat conjunctivitis and orally for the treatment of bacterial infections of the urinary tract; 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid, C16H18FN3O3.