procto-, proct-

1. A ring-shaped synchrotron that accelerates protons to energies of several billion electron volts.
2. A circular, very high-energy particle accelerator that accelerates protons through the action of magnetic fields and a high-frequency electric field.

1. A contracting gas cloud in the embryonic of beginning stage of a star formation before the onset or beginning of thermonuclear reactions in its interior.
2. A celestial object made of a contracting cloud of interstellar medium (mostly hydrogen gas) which eventually becomes a main-sequence star.

Less massive protostars may take hundres of millions of years to evolve into stars; massive ones contract more quickly and may take only a few hundred thousand years to evolve.