glower (v.)youdaoicibaDictYouDict
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.
thunder (v.)youdaoicibaDictYouDict
13c., from Old English þunrian, from the source of thunder (n.). Figurative sense of "to speak loudly, threateningly, or bombastically" is recorded from mid-14c. Related: Thundered; thundering. Compare Dutch donderen, German donnern.