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]