mid-14c., "to shine;" c.1500, "to stare with wide eyes," perhaps from a Scandinavian source (compare Norwegian dialectal glora "to glow, gleam; stare"), or related to Middle Dutch gluren "to leer;" in either case from Proto-Germanic *glo- (see glow, v.), root of Old English glowan "to glow," which influenced the spelling of this word. Meaning "to look angrily, look intently and threateningly, scowl" is from 18c. Related: Glowered; glowering. As a noun, 1715, "an angry or threatening stare," from the verb.