The Collaborative International Dictionary of English v.0.48:
Louse \Louse\ (lous), n.; pl. Lice (l[imac]s). [OE. lous, AS.
l[=u]s, pl. l[=y]s; akin to D. luis, G. laus, OHG. l[=u]s,
Icel. l[=u]s, Sw. lus, Dan. luus; perh. so named because it
is destructive, and akin to E. lose, loose.] (Zool.)
1. Any one of numerous species of small, wingless, suctorial,
parasitic insects belonging to a tribe (Pediculina), now
usually regarded as degraded Hemiptera. To this group
belong of the lice of man and other mammals; as, the head
louse of man (Pediculus capitis), the body louse
(Pediculus vestimenti), and the crab louse (Phthirius
pubis), and many others. See Crab louse, Dog louse,
Cattle louse, etc., under Crab, Dog, etc.
2. Any one of numerous small mandibulate insects, mostly
parasitic on birds, and feeding on the feathers. They are
known as Mallophaga, or bird lice, though some occur on
the hair of mammals. They are usually regarded as degraded
Pseudoneuroptera. See Mallophaga.
3. Any one of the numerous species of aphids, or plant lice.
4. Any small crustacean parasitic on fishes. See
Branchiura, and Ichthvophthira.
Note: The term is also applied to various other parasites;
as, the whale louse, beelouse, horse louse.
Louse fly (Zool.), a parasitic dipterous insect of the
group Pupipara. Some of them are wingless, as the bee
Louse mite (Zool.), any one of numerous species of mites
which infest mammals and birds, clinging to the hair and
feathers like lice. They belong to Myobia,
Dermaleichus, Mycoptes, and several other genera.