Definition of "tau" [tau]

• The 19th letter of the Greek alphabet. See Table at alphabet. (noun)
• An elementary particle of the lepton family, having a mass about 3,550 times that of the electron, a negative electric charge, and a mean lifetime of 3 × 10-13 seconds. See Table at subatomic particle. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Alzheimer's is marked by deposits of beta-amyloid protein in the brain, and knotty protein structures in the nerves themselves called tau tangles."
• "Eventually another small protein, called tau, also starts to crystallize in this way to form "tangles.""
• "Among the possible advances in early detection are chemical tracers, some of which tag clumps of a sticky substance in the brain called amyloid, and others that mark amyloid and a protein called tau—both thought to contribute to the disease."