Astronomy Answers
From the Astronomical Dictionary

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The description of the word you requested from the astronomical dictionary is given below.

the star ⇒

astèr = [Greek] star

A star is a ball of (mostly) hydrogen gas that is so massive that it

1. is held together by its own gravitation.
2. has such a high gas pressure and temperature in its center that nuclear fusion of hydrogen to helium occurs there, which provides the energy that makes the star shine brightly.