Webster's New World Medical Dictionary

hirsute
Having an overabundance of hair.
hirsutism
Having excessive facial and bodily
hair. Hirsutism can be a side effect of certain med-
ications (such as prednisone) or reflect an underly-
ing hormonal imbalance.
hirudin
An anticlotting agent that prevents blood
clots from traveling through the bloodstream to clog
up a vessel (thromboembolic complications).
Hirudin is the main chemical in the secretion of
leeches that allows them to suck out blood freely
from the body after they attach to the skin.
Desirudin and lepirudin (brand name: Refludan)
are genetically engineered recombinant forms of
hirudin.
His disease
See 
trench fever.
histamine
A substance that plays a major role in
many allergic reactions, dilating blood vessels and
making the vessel walls abnormally permeable.
Histamine is part of the body’s natural allergic
response to substances such as pollens.
Antihistamines work by preventing the release of
histamine from certain cells (mast cells) thereby
blocking the allergic reaction.
histamine cephalalgia
See 
cluster headache.
histiocyte
A type of white blood cell, also called
a macrophage, that is created by bone marrow.
Histiocytes usually stay in place, but when they are
stimulated by infection or inflammation, they
become active, attacking bacteria and other foreign
matter in the body. See also 
histiocytosis.
histiocytosis
One of several disorders in which
histiocytes start to multiply and proliferate abnor-
mally. The result can be tissue damage, pain, the
development of tumor-like lumps, fatigue, and other
symptoms. If histiocytosis affects the pituitary gland,
diabetes insipidus may also develop. Treatment
includes radiation and chemotherapy, although for
reasons unknown, some cases of histiocytosis go
into remission without treatment.