Webster's New World Medical Dictionary

appendix
A small outpouching from the begin-
ning of the large intestine.
appendix epididymis
A small cystic projection
from the surface of the epididymis (a structure
within the scrotum that is attached to the backside
of the testis), which represents a remnant of the
embryologic mesonephros.
appendix epiploica
A finger-like projection of
fat attached to the colon.
appendix testis
A small solid projection of tis-
sue on the outer surface of the testis, which is a
remnant of the embryologic mullerian duct.
apposition 1
The act of adding or accretion.
Growth by apposition is characteristic of many tis-
sues in the body by which nutritive matter from the
blood is transformed on the surface of an organ into
a solid unorganized substance.
2
The act of put-
ting things in juxtaposition or side by side. To lose a
pair of apposed teeth is to lose teeth that are next to
each other. Also known as juxtaposition.
apraxia
The inability to execute a voluntary
motor movement despite being able to demonstrate
normal muscle function. Apraxia is not related to a
lack of understanding or to any kind of physical
paralysis; rather, it is caused by a problem in the
cortex of the brain.
apraxia of speech
A severe speech disorder
characterized by an inability to speak or a severe
struggle to speak clearly. Apraxia of speech occurs
when the oral-motor muscles do not or cannot obey
commands from the brain or when the brain cannot
reliably send those commands. Apraxia of speech is
caused by damage to the Broca area in the brain.
See also 
dyspraxia of speech.
APS
Antiphospholipid syndrome.
apthous ulcer
See 
canker sore.
aqueduct
A channel for the passage of fluid.