Oxford Reference Online
Includes the Oxford Companion to the Body; Dictionary of Dentistry; Dictionary of Food and Nutrition; Concise Medical Dictionary; A-Z of Medicinal Drugs; Oxford Companion to Medicine; Dictionary of Nursing; A-Z of Plastic Surgery; Dictionary of Public Health; Oxford Dictionary of Sports Science & Medicine. Strong UK bias.
Useful for quick reference and basic overviews; quotes. Not intended for in-depth clinical practice.