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nineteenth letter of the Greek alphabet, from Hebrew taw, last letter of the Hebrew alphabet, literally "sign, mark."
Symbol τ The 19th letter of the Greek alphabet.
elementary subatomic particle similar to the electron but approximately 3,500 times heavier. Like the electron and the muon, the tau is an electrically charged member of the lepton family of subatomic particles; the tau is negatively charged, while its antiparticle is positively charged