neu·tri·no 
(n-trēnō, ny-)
(n-trēnō, ny-)n. pl. neu·tri·nos
Any of three electrically neutral leptons (the electron neutrino, muon neutrino and tau neutrino—one in each of the three generations of elementary fermions) that have small or very small masses.
[Italian, from neutrino, little neutral one : neutro, neuter, neutral (from Latin neuter, neutr-, neuter; see NEUTER) + -ino, dimutive suff. (from Latin -īnus, adj. suff.; see -INE1). Coined by Enrico Fermi on the model of Italian neutrone, neutron, taken as the augmentative of Italian neutro.]