WordReference Random House Unabridged Dictionary of American English © 2026
pro•to•star
(prō′tō stär′),USA pronunciation n. [Astron.]
- Astronomyan early stage in the evolution of a star, after the beginning of the collapse of the gas cloud from which it is formed, but before sufficient contraction has occurred to permit initiation of nuclear reactions at its core.
- proto- + star 1945–50