leptonica is the Italian word for "leptonic", which is an adjective that refers to three very similar families of fundamental particles, called leptons, of which the electron and its neutrino comprise the one most familiar to us.
The name lepton is derived from the Greek, meaning "light" particle. (This is in contrast to the "heavy" particles, such as the proton.) The name was chosen in the 1940s by Abraham Pais, a particle physicist who has written several excellent books on the history of physics of the 20th century, including technical biographies of Albert Einstein and Niels Bohr.
To learn a little bit about elementary particles, go to the primer .
