1620s, "marked by grandeur," probably a shortening of earlier splendidious (early 15c.), from Latin splendidus "bright, shining, glittering; sumptuous, gorgeous, grand; illustrious, distinguished, noble; showy, fine, specious," from splendere "be bright, shine, gleam, glisten," from PIE *splend- "to shine, glow" (cognates: Lithuanian splendziu "I shine," Middle Irish lainn "bright"). An earlier form was splendent (late 15c.). From 1640s as "brilliant, dazzling;" 1640s as "conspicuous, illustrious; very fine, excellent." Ironic use (as in splendid isolation, 1843) is attested from 17c.