tau

noun

ˈtau̇  ˈtȯ 

1

: the 19th letter of the Greek alphabet see Alphabet Table

2

: a short-lived elementary particle of the lepton family that exists in positive and negative charge states and has a mass about 3500 times greater than an electron

called also tau particle

3

: 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

Examples of tau in a Sentence

Recent Examples on the Web

Compared to those with low vitamin D levels, participants with high vitamin D levels had less tau buildup in their fifties, including in regions of the brain where this protein tends to accumulate first in individuals who develop dementia, the study found. —Emily Kay Votruba, EverydayHealth.com, 1 Apr. 2026

In 2021, Gefen and her colleagues published research in the journal Cerebral Cortex showing that super-agers are resistant to neurofibrillary, or tau, tangles, which are abnormal protein buildups tied to Alzheimer’s. —Lindsey Leake, NBC news, 26 Feb. 2026

Research efforts are ongoing, with scientists exploring therapies that target the underlying tau pathology. —Mill Etienne, Forbes.com, 23 Feb. 2026

The facility will produce a lot of tau particles and charm quarks, partly to study whether taus ever shape-shift into muons or electrons. —Quanta Magazine, 26 Jan. 2026

Word History

Etymology

Middle English taw, from Latin tau, from Greek, of Semitic origin; akin to Hebrew tāw taw

First Known Use

14th century, in the meaning defined at sense 1

Phrases Containing tau

• tau cross

Kids Definition

tau

noun

ˈtau̇ 

ˈtȯ

: the 19th letter of the Greek alphabet

—Τ or τ

Medical Definition

tau

noun

ˈtau̇  ˈtȯ 

: 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

called also tau protein