splendid: [17] Splendid comes via French splendide from Latin splendidus, a derivative of the verb splendēre ‘shine’. This went back ultimately to the Indo-European base *splēnd- or *plēnd- ‘bright’, which also produced Old Lithuanian splendeti ‘shine’ and Welsh llathru ‘polish’. Amongst the derivatives adopted by English are resplendent [15], splendiferous [15] (from splendiferus, a medieval alteration of late Latin splendōrifer, literally ‘bearing brightness’, hence ‘full of splendour’ – its modern use, as a jocular alternative to splendid, is a 19th-century American innovation), and splendour [15]. => resplendent
splendid (adj.)
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.