1. the 19th letter of the greek alphabet. see table at alphabet.
2. 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.

1. 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. A Τ-shaped sign or structure; a st. anthony's cross, sometimes considered as a sacred symbol.
3. A tau meson, now usually known as a kaon.
4. an unstable heavy lepton, which decays into a muon or electron; a tauon.
5. A type of protein used to stabilise microtubules.

1. the nineteenth letter (Τ, τ) of the greek alphabet, equivalent to english t.
2. the common american toadfish; -- so called from a marking resembling the greek letter tau (τ).

1. in ichthyology, the toadfish, Batrachus tau.
2. in entomology: A beetle.
3. A phalænid moth.
4. A fly.
5. in heraldry, same as tau-cross.

1. the 19th letter of the greek alphabet