Old English sunne "the sun," from Proto-Germanic *sunno (source also of Old Norse, Old Saxon, Old High German sunna, Middle Dutch sonne, Dutch zon, German Sonne, Gothic sunno "the sun"), from PIE *s(u)wen-, alternative form of root *sawel- "the sun."
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.
c. 1600, "a garment or assemblage of garments," originally any clothing, especially that appropriate to rank or to some ceremony; the specific sense of "woman's garment consisting of a skirt and waist" is recorded by 1630s, with overtones of "made not merely to clothe but to adorn." Dress rehearsal first recorded 1828.