Webster's New World Medical Dictionary

acute thrombocytopenic purpura
Sudden
onset of low blood platelet levels, with bleeding into
the skin and elsewhere. Abbreviated ATP. ATP can
have many causes; for example, it can be a poten-
tially serious complication during the acute phase of
measles infection.
acute-phase protein
A protein whose plasma
concentrations increase during certain inflamma-
tory disorders. Perhaps the best-known acute-phase
protein is C-reactive protein (CRP).
acyclovir
A potent antiviral drug or medication
(brand name: Zovirax) that works against several
human herpes viruses, Epstein-Barr virus, herpes
zoster, varicella (chickenpox), cytomegalovirus,
and other viruses. It is part of the AIDS drug AZT.
See also 
AZT.
ad-
Prefix indicating toward or in the direction of.
For example, adduction is the movement of a limb
toward the midline of the body, and adrenal literally
means “toward the kidney.”
ad lib
Abbreviation of the Latin phrase 
ad libi-
tum,
meaning “as much as one desires” or “at your
discretion.” See also Appendix A, “Prescription
Abbreviations.”
ADA 1
American Dental Association, a professional
organization for dentists. Its Council on Dental
Education and Commission on Dental Accreditation
are responsible for accrediting schools of dentistry
and allied professions.
2
American Diabetes
Association, a nonprofit health organization that
sponsors diabetes research, provides information
about diabetes and diabetes prevention to patients
and others, and advocates for improved treatment of
people with diabetes.
3
Adenosine deaminase.
Adam’s apple
The familiar feature on the front of
the neck that is the forward protrusion of the thy-
roid cartilage, the largest cartilage of the larynx. It
tends to enlarge at adolescence, particularly in
males. It is usually said to take its name from the
extrabiblical story that a piece of the forbidden fruit
stuck in Adam’s throat.