Webster's New World Medical Dictionary

aftercare
Medical care and instructions for
patients after leaving a medical facility.
agammaglobulinemia
Total or near-total
absence of infection-fighting antibodies belonging
to the class called gamma globulins.
Agammaglobulinemia can be due to certain genetic
diseases or caused by acquired diseases, including
AIDS.
agenesis
Lack of development. For example, age-
nesis of a toe means the toe failed to form.
agenesis, sacral
See 
caudal regression syn-
drome.
agenesis of the gallbladder
A condition in
which the gallbladder fails to develop. It occurs in 1
in about every 1,000 people, usually without addi-
tional birth defects.
agent, antihypertensive
See 
antihypertensive.
agent, anti-infective
See 
anti-infective.
Agent Orange
An herbicide and defoliant con-
taining 2,4-D and 2,4,5-T, as well as trace
amounts of dioxin. Agent Orange was used as a
defoliant in the Vietnam War. There has been con-
cern about Agent Orange potentially causing cancer
and birth defects.
age-related macular degeneration
See 
mac-
ular degeneration.
ageusia
An inability to taste sweet, sour, bitter, or
salty substances. People who can taste sweet, sour,
bitter, or salty substances but have a reduced ability
to do so are said to have hypogeusia.
aggressive 1
In cancer medicine, quickly grow-
ing or tending to spread rapidly. For example, an
aggressive tumor.
2
In psychiatry, having a ten-
dency to aggression or belligerent behavior.
aggressive fibromatosis
See 
desmoid tumor.
agnosia
An inability to recognize sensory inputs
such as light, sound, and touch). Agnosia is typically
a result of brain injury. For example, damaging the
back part of the brain can cause visual agnosia
(inability to properly recognize objects by sight).
agonist
A substance that acts like another sub-
stance and therefore stimulates an action. Agonist is
the opposite of antagonist. Antagonists and agonists
are key players in the chemistry of the human body
and in pharmacology.
agoraphobia
An abnormal and persistent fear of
public places or open areas, especially those from
which escape could be difficult or in which help
might not be immediately accessible. Persons with
agoraphobia frequently also have panic disorder.
People with mild agoraphobia often live normal
lives by avoiding anxiety-provoking situations. In the
most severe agoraphobia, the victims may be inca-
pacitated and homebound. Agoraphobia tends to
start in the mid to late 20s, and the onset may
appear to be triggered by a traumatic event.
agranulocytosis
A marked decrease in the num-
ber of granulocytes (neutrophils). Agranulocytosis
results in frequent chronic bacterial infections of
the skin, lungs, throat, and other areas. It can be an
inherited genetic condition or acquired as, for
example, in leukemia. See also 
agranulocytosis,
infantile genetic; granulocytopenia; severe con-
genital neutropenia.