c. 1300, "fear, terror, state of alarm produced by a sudden disturbance," from Old French affrai, effrei, esfrei "disturbance, fright," from esfreer (v.) "to worry, concern, trouble, disturb," from Vulgar Latin *exfridare, a hybrid word meaning literally "to take out of peace."
The first element is from Latin ex "out of" (see ex-). The second is Frankish *frithu "peace," from Proto-Germanic *frithuz "peace, consideration, forbearance" (source also of Old Saxon frithu, Old English friðu, Old High German fridu "peace, truce," German Freide "peace"), from a suffixed form of PIE root *pri- "to be friendly, to love."
Meaning "breach of the peace, riotous fight in public" is from late 15c., via the notion of "disturbance causing terror." The French verb also entered Middle English, as afrey "to terrify, frighten" (early 14c.), but it survives almost exclusively in its past participle, afraid (q.v.).