Old English glowan "to glow, shine as if red-hot," from Proto-Germanic *glo- (cognates: Old Saxon gloian, Old Frisian gled "glow, blaze," Old Norse gloa, Old High German gluoen, German glühen "to glow, glitter, shine"), from PIE *ghel- (2) "to shine," with derivatives referring to bright materials and gold (see glass, n., also glint, glad, etc.). Figuratively from late 14c. Related: Glowed; glowing. Swedish dialectal and Danish glo also have the extended sense "stare, gaze upon," which is found in Middle English.

mid-15c., "glowing heat," from glow (v). Meaning "a flush of radiant feeling" is from 1793.