c. 1200, frensh, frenche, "pertaining to France or the French," from Old English frencisc "French," originally "of the Franks," from franca, the people name (see Frank). A similar contraction of -ish is in Dutch, Scotch, Welsh, suggesting the habit applies to the names of only the intimate neighbors.
In some provincial forms of English it could mean simply "foreign." Used in many combination-words, often dealing with food or sex: French dressing (by 1860); French toast (1630s); French letter "condom" (c. 1856, perhaps on resemblance of sheepskin and parchment), french (v.) "perform oral sex on," and French kiss (1923) all probably stem from the Anglo-Saxon equation of Gallic culture and sexual sophistication, a sense first recorded 1749 in the phrase French novel. (In late 19c.-early 20c., a French kiss was a kiss on each cheek.) French-Canadian is from 1774; French doors is by 1847. To take French leave, "depart without telling the host," is 1771, from a social custom then prevalent. However, this is said to be called in France filer à l'anglaise, literally "to take English leave."