I. ˈtau̇, ˈtȯ noun
( -s )
Etymology: Greek, of Semitic origin; akin to Hebrew tāw sign, cross, taw (letter)
1.
a. : the 19th letter of the Greek alphabet — symbol T or τ; see alphabet table
b. : taw IV
2. : a T-shaped mark or object (as a St. Anthony's cross, a pastoral staff, or an ankh)
II. noun
1. also tau particle : a short-lived elementary particle of the lepton family that exists in positive and negative charge states and has a mass about 3500 times heavier than an electron
2. : a protein that binds to and regulates the assembly and stability of neuronal microtubules and that is found in an abnormal form as the major component of neurofibrillary tangles