Etymology 1 
From Middle English flayen, flaien, fleien, from Old English *flīeġan ("to cause to fly, put to flight, frighten"; found only in compounds: āflīeġan), from Proto-Germanic *flaugijaną (“to let fly, cause to fly”), causitive of Proto-Germanic *fleuganą (“to fly”), from Proto-Indo-European *plew-k-, *plew- (“to run, flow, swim, fly”). Cognate with Old High German arflaugjan ("to frighten, cause to flee"; whence Middle High German ervlougen (“to put to flight, drive away, expel”)), Icelandic fleygja (“to throw away, discard”), Gothic 𐌿𐍃-𐍆𐌻𐌰𐌿𐌲𐌾𐌰𐌽 (us-flaugjan, “to cause to fly”).
Alternative forms 
- (transitive, UK dialectal, Northern England, Scotland) To cause to fly; put to flight; drive off (by frightening).
- (transitive, UK dialectal, Northern England, Scotland) To frighten; scare; terrify.
- (intransitive, UK dialectal, Northern England, Scotland) To be fear-stricken.
Derived terms 
flay (plural flays)
- (UK dialectal, Northern England, Scotland) A fright; a scare.
- (UK dialectal, Northern England, Scotland) Fear; a source of fear; a formidable matter; a fearsome or repellent-looking individual.