(Webster's New World Dictionary)

e|lec·tron (e lek' trän) n. [coined (1891) by G. J. Stoney, Ir physicist < ELECTR(IC) + -ON]
Gr proton, neut. of protos, first: see PROTO-
| a stable elementary particle that forms a part of all atoms and has a negative charge of 1.602 x 10(-19) coulomb: the mass of an electron is about 1/1837 that of a proton with a rest mass of 9.10939 x 10(-28) gram, and the number of electrons circulating around a nucleus is equal to the number of positive charges on the nucleus; negatron.

proton (pro' tän) n. < Gr proton, neut. of protos, first: see PROTO-
| an elementary particle found in the neucleus of all atoms and comprising the atomic neucleus of the protium isotope of hydrogen: it carries a unit positive charge equal to the negative charge of an electron and has a mass of 1.673 x 10(28) gram, approximately 1836 times that of an electron: the atomic number is equal to the number of protons in its neucleus.

neutron (nõõ' trän, nyõõ-) n. [NEUTR(AL) + -ON]
| an uncharged elementary particle of an atom with approximately the same mass as a proton: a free neutron, as in neuclear fission, interacts strongly with nuclei, is readily absorbed, and decays into a proton, an electron and a neutrino with a half-life of c. 12 minutes.