unbound

Etymology

verb

1. simple past and past participle of unbind

adj

1. Not bound; not tied up.
   The hostages' hands were left unbound.
2. Without a binding.
   an unbound book
   Beneath an old ebony table were two long carved oak chests. I lifted the lid of one, and at the top was a once-white surplice covered with dust, and beneath was a mass of tracts — Commonwealth Quartos, unbound — a prey to worms and decay. 1880, William Blades, The Enemies of Books, page 40
3. (nuclear physics, of an atomic nucleus) Lying beyond the proton or neutron drip line; having a negative particle separation energy; capable of decaying by the spontaneous exothermic emission of one or more nucleons.
   Helium-2 is unbound, as it is energetically favorable for it to split into two separate protons.