Medical Dictionary Online - http://www.online-medical-dictionary.org/
A free online medical dictionary search engine for definitions of medical terminology, pharmaceutical drugs, healthcare equipment, health conditions, medical devices, specialty terms and medical abbreviations.
VoyCabulary - http://www.voycabulary.com/
Free online web Dictionary and Thesaurus linking reference tool. Transforms words on any webpage into links to definition and word lookups in Dictionaries or Thesauruses.