You know that you when you glow you radiate: light comes from you, and warmth too. But are you also a glower when you glower?
I won’t say which has a greater glimmer of glamour, but while a beau or paramour may glow, a dowager (or a lout) will glower. But what is glowering anyway? Do we think of it as like lowering clouds, a storm brewing in the face? Or do we see it as two glowing-hot coals, one in each eye socket?
Survey says… it’s the coals. To glower is to glare, and we know that an overly bright light glares, too. And, yes, if you’re looking at these gl– words about lights and looks, warm or hot, and wondering if they’re related, the answer is that these ones do seem to be. It’s not completely certain, but glower appears to be related to glow (the different pronunciations of ow notwithstanding); if you look around the linguistic neighbourhood, you also find a Danish word glo meaning ‘glower’ or ‘glare’ that is descended from an Old Norse word meaning ‘glow’. And glow and glare are pretty surely from the same root. (None of this is to say that glass, gleam, and several other gl– words having to do with optical effects are also etymologically related, but there’s clearly a clustering effect whereby we tend to associate gl– words with things optical and vice versa. I may have written a master’s thesis on this.)
So. When you glower, you are a glow-er; your eyes glow like hot coals, ready not to warm but to singe. There is even a now-disused sense of glow current from the 1300s to the 1800s that means ‘stare’. Glower is newer; it came from Scots in the 1500s to mean ‘look wide-eyed with surprise’ and by the 1700s gained the current ‘look angrily’ sense. And somewhere in there it lost its flower to a power mower and started sounding less like goer and more like hour, more like shower and less like shower. This is a glow that prefers to assault rather than to reveal.