sun (n.)
Old English sunne "sun," from Proto-Germanic *sunnon (cognates: Old Norse, Old Saxon, Old High German sunna, Middle Dutch sonne, Dutch zon, German Sonne, Gothic sunno "the sun"), from PIE *s(u)wen- (cognates: Avestan xueng "sun," Old Irish fur-sunnud "lighting up"), alternative form of root *saewel- "to shine; sun" (see Sol).

Old English sunne was feminine (as generally in Germanic), and the fem. pronoun was used in English until 16c.; since then masc. has prevailed. The empire on which the sun never sets (1630) originally was the Spanish, later the British. To have one's place in the sun (1680s) is from Pascal's "Pensées"; the German imperial foreign policy sense (1897) is from a speech by von Bülow.
sun (v.)
1510s, "to set something in the sun," from sun (n.). Intransitive meaning "expose oneself to the sun" is recorded from c.1600. Sun-bathing is attested from c.1600.