galayoudaoicibaDictYouDict[gala 词源字典]
gala: [17] Gala comes ultimately from Arabic khil’a, which denoted an ‘especially fine garment given as a presentation’. This original meaning persisted through Spanish gala and into Italian and French gala, from one or other of which English got it (‘Whereupon this King and the whole Court put on Galas [special festive attire]’, Cabala sive scrinia sacra 1654) and survived into the 19th century (‘Apparelled on Sunday morning in gala, as if for the drawingroom, he constantly marched out all his household to the parish church’, George Bancroft, History of the United States 1876).

Nowadays, however, all that remains is the extended sense ‘festive occasion’, first recorded in the late 18th century.
[gala etymology, gala origin, 英语词源]
gala (n.)youdaoicibaDictYouDict
1620s, "festive dress or attire" (obsolete), from French en gala, perhaps from Old French gale "merriment," from galer "rejoice, make merry" (see gallant). Klein suggests the French word is from Italian gala (as in phrase vestito di gala "robe of state"), perhaps from Arabic khil'a "fine garment given as a presentation." Sense of "festive occasion" (characterized by display of finery) first recorded 1777. Quasi-adjectival use in gala day "day of festivities," etc.