the world > matter > physics > atomic physics > particle physics > particle avoiding strong interaction > electron > [adjective] > of electron: able to move unrestrictedly (2)
unbound1697
Of substances: In a loose or free state. Also of a particle: = free, adj. 11b.
free1895
Physics and Chemistry. Designating an electron or other particle which is not bound to another atom, molecule, etc., and is therefore able to move…