lambda

noun

1. the eleventh letter of the Greek alphabet (Λ, λ)
2. Particle Physics an uncharged hyperon with a mass of c. 1,115.68 MeV/c, which is c. 2,183 times the mass of an electron: it decays very rapidly, usually into a nucleon and a pion
   sometimes called lambda particle or lambda hyperon

Origin: Gr < Sem, as in Heb lāmedh, lamed