left brain

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

• noun The cerebral hemisphere to the left of the corpus callosum, controlling activities on the right side of the body, and in humans, usually controlling speech and language functions.

from the GNU version of the Collaborative International Dictionary of English.

• noun The left cerebral hemisphere of the brain; in humans, it controls motor activity on the right side of the body, and in most people is the primary location for control of language, logic, and mathematical thought.

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

• noun the cerebral hemisphere to the left of the corpus callosum that controls the right half of the body