Gael n.

1670s, "of or pertaining to the French," from Latin Gallicus "pertaining to Gaul or the Gauls," from Latin Gallia "Gaul" and Gallus "a Gaul" from a native Celtic name (see Gaelic), though some connect the word with prehistoric West Germanic *walkhoz "foreigners" (see Welsh). Originally used in English rhetorically or mockingly for "French." The cock as a symbol of France is based on the pun of Gallus "a Gaul" and Latin gallus "cock" (see gallinaceous). Earlier was Gallican (1590s).

It means not simply 'French,' but 'characteristically', 'delightfully', 'distressingly', or 'amusingly' 'French' ... not 'of France', but 'of the typical Frenchman'. [Fowler]

As "of or pertaining to the ancient Gauls" from 1796.

Biblical epistle, from Galatia, name of an ancient inland region in Asia Minor, from Greek Galatia, based on Gaul, in reference to the Gaulish people who conquered the region and settled there 3c. B.C.E. In Latin Gallograeci, hence Middle English Gallocrecs "the Gallatians."