Amoxicillin: An antibiotic of the penicillin type that is effective against different bacteria such as Haemophilus influenzae, Neisseria gonorrhoea, Escherichia coli, Pneumococci, Streptococci, and certain strains of Staphylococci, particularly infections of the middle ear, tonsillitis, throat infections, laryngitis, bronchitis, and pneumonia. Amoxicillin is also used in treating urinary tract infections, skin infections, and gonorrhea. The brand names are Amoxil, Polymox, and Trimox. A generic version is available.