"impressed with fear, fearful," early 14c., originally the past participle of the now-obsolete Middle English verb afray "frighten," from Anglo-French afrayer, 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 friu, Old High German fridu "peace, truce," German Freide "peace"), from a suffixed form of PIE root *pri- "to be friendly, to love."
A rare case of an English adjective that never stands before a noun. Because it was used in the King James Bible, it acquired independent standing and thrived while affray faded, and it chased off the once more common afeared. Colloquial sense in I'm afraid "I regret to say, I suspect" (without implication of fear, as a polite introduction to a correction, admission, etc.) is first recorded 1590s.
Her blue affrayed eyes wide open shone [Keats, "The Eve of St. Agnes," 1820]