Real Dictionary

sun
If you are sunning yourself, you are sitting or lying in a place where the sun is shining on you.
singular noun: The sun is the ball of fire in the sky that the Earth goes round, and that gives us heat and light.
uncountable noun: You refer to the light and heat that reach us from the sun as the sun.

Sun in American English
Sunday
noun: the star that is the central body of the solar system, around which the planets revolve and from which they receive light and heat: its mean distance from the earth is about 93 million miles (150 million km), its diameter about 864,000 miles (1.4 million

sun in American English 1
the self-luminous, gaseous central star of the solar system: magnitude, -26; mean distance from the earth, c. 149.6 million km (c. 93 million mi); diameter, c. 1.4 million km (c. 864,000 mi); mass, c. 332,000 times that of the earth; volume, c. 1.3 millio

sun in American English 2
an East Indian annual plant ( Crotalaria juncea) of the pea family, grown for its bast fiber used in making rope, bagging, cigarette papers, etc.

sun in British English
noun: the star at the centre of our solar system. It is a gaseous body having a highly compressed core, in which energy is generated by thermonuclear reactions (at about 15 million kelvins), surrounded by less dense radiative and convective zones serving to tra

Sun.
Sun. is a written abbreviation for Sunday.

Sun. in American English
Sunday

Sun. in British English
abbreviation for: Sunday