sheep tick

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A tick (Ixodes ricinus) that infests sheep and other vertebrates, including humans.

from The Century Dictionary.

• noun A pupiparous dipterous insect of the family Hippoboscidæ, Melophagus ovinus, which infests sheep.
• noun Same as sheep-louse, 2.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun parasitic on sheep and cattle as well as humans; can transmit looping ill in sheep (acute viral disease of the nervous system); a vector for Lyme disease spirochete
• noun wingless fly that is an external parasite on sheep and cattle
• noun parasitic on sheep and cattle as well as humans; can transmit looping ill in sheep (acute viral disease of the nervous system); a vector for Lyme disease spirochete
• noun wingless fly that is an external parasite on sheep and cattle