tetracycline /ˌtɛ.tɹəˈsaɪ.kliːn/ noun2 •A yellow crystalline broad-spectrum antibiotic C₂₂H₂₄N₂O₈ produced by streptomyces or synthetically. •Any of a large group of antibiotics with the same general structure derived from tetracene with many hydroxyl and other groups. formstetracyclines