An Etymological Dictionary of Astronomy and Astrophysics

The difference between the isotopic mass of a nuclide and its mass number divided by its mass number. The packing fraction is a measure of the stability of the nucleus.

Etymology (EN): Packing, from the verb pack “to put together in a pack,” from the noun pack, from M.E. pak, packe, from M.D. pac or perhaps M.L.G. pak; → fraction.

Etymology (PE): Barxé, → fraction; anbâštegi quality noun of anbâštan, anbârdan “to fill, to replete;” Mid.Pers. hambāridan “to fill;” from Proto-Iranian *ham-par-, from prefix ham- + par- “to fill;” cf. Av. par- “to fill,”
parav-, pauru-, pouru- “full, much, many;”
O.Pers. paru- “much, many;” Mid.Pers. purr “full;” Mod.Pers. por “full, much, very;”
PIE base *pelu- “full,” from *pel- “to be full;” cf. Skt. puru- “much, abundant;”
Gk. polus “many,” plethos “great number, multitude;” O.E. full.