Webster's New World Medical Dictionary

labial
Pertaining to a lip.
labial sound
A sound requiring the participation
of one or both lips. Also known simply as labial. All
labials are consonants. Bilabial sounds, such as
“p,” involve both lips, whereas labiodental sounds,
such as “v,” involve the upper teeth and lower lip.
labile
Unstable. For example, labile blood pres-
sure is blood pressure that abnormally increases
and decreases frequently.
labile diabetes
See 
diabetes, labile.
labium
The singular form of labia.
labor
Childbirth, the process of delivering a baby
and the placenta, membranes, and umbilical cord
from the uterus to the vagina to the outside world.
During the first stage of labor (which is called dila-
tion), the cervix dilates fully to a diameter of about
10 cm (2 inches). The first stage of labor is divided
into two phases: the latent phase and the active
phase. In the latent phase, contractions become
progressively more coordinated and the cervix
dilates to 4 cm (approximately 1.5 inches). The
latent phase averages about 8 hours for a nullipara
(a woman having her first baby) and 5 hours for a
multipara (a woman having a subsequent baby). In
the active phase, the cervix becomes fully dilated
and the presenting part of the baby descends into
the midpelvis. The active phase averages about 5
hours for a nullipara and 2 hours for a multipara.
In the second stage (which is called expulsion), the
baby moves out through the cervix and vagina to be
born. Expulsion generally lasts 2 hours for a nulli-
para and l hour for a multipara. The third stage of
labor begins with the delivery of the baby and ends
when the placenta and membranes are expelled.
Also known as parturition and childbirth.
laboratory
A place for doing tests and research
procedures, and for preparing chemicals and some
medications. Also known as lab.
labyrinth
The maze of canals in the inner ear.
The delicate membranous canals of the labyrinth
are enclosed and protected by a bony chamber that
is referred to as the bony labyrinth. The labyrinth is
the portion of the ear that is responsible for sensing
balance.
labyrinthitis
Inflammation of the labyrinth of the
ear, which can be accompanied by vertigo.
Labyrinthitis has many potential causes including
virus infection, Ménière’s disease, and autoimmune
disease.