A Quick and Simple Dictionary

tau

1. Noun.  The name of the letter T/τ in the Greek, Hebrew and ancient Semitic alphabets, being the nineteenth letter of the Classical and Modern Greek, the twentieth letter of Old and Ancient Greek.
2. Noun.  A (polytonic, Τ) -shaped sign or structure; a St. Anthony's cross, sometimes considered as a sacred symbol.
3. Noun.  (context, particles) A tau meson, now usually known as a kaon.
4. Noun.  An unstable heavy lepton, which decays into a muon or electron.