Here is a link to a great Medical Dictionary:
It comes with a caution though. Use it to find the meaning of words you hear. When dealing with medical people, you are always better to "describe" NOT "define." Patients who "medicalize" their conditions frequently get things overlook or are though to be "Somaticizing" their condition. Describe what is going on and more importantly us "what/when/then" statements. Its more helpful to your treatment to describe "what" is happening, when it happens, "then" what it does.