Lambda Tauri (λ Tau / λ Tauri) is a triple star system in the constellation Taurus. It has the traditional name Elthor (Althor, Althaur, Al Thaur), which is Arabic for "The Bull", derived from the title Ath-Thawr Ath-Thurayya (‏الثور الثريا), meaning "The Bull of the Pleiades".

The primary component, Lambda Tauri A, is a blue-white B-type main sequence dwarf with a mean apparent magnitude of +3.41. It has a luminosity of about 4,000 times that of the Sun and a radius of 6.6 times solar. The companion is a white A-type subgiant of 5.5 solar radii and 95 solar luminosities. They orbit around a common centre of gravity once every 3.95 days. The spatial separation between these two stars is measured at 0.1 astronomical unit.

Because the system is an eclipsing binary its brightness varies from magnitude +3.37 to +3.91 as first one star and then the other pass in front of its companion. The system has a third, dimmer star with an orbital period of 33 days. The Lambda Tauri system is approximately 370 light years from Earth.

It, along with δ Librae, was the first star on which
rotational line broadening, Frank Schlesinger, Monthly Notices of the Royal Astronomical Society, Vol. 71, p.719-719.
was observed, by Frank Schlesinger in 1909.