Meaning of “sun” - Learner’s Dictionary

sun

noun us uk /sʌn/
the sun

A1 the large, bright star that shines in the sky during the day and provides light and heat for the Earth:

The sun rises in the East and sets in the West.

More examples

A1 [ U, no plural ] the light and heat that comes from the sun:

I can't sit in the sun for too long.

(Definition of “sun noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)