Other forms: brightened, brightening, brightens
To brighten something is to make it lighter, or fuller of light. You brighten a dark photo with a slider on your phone, brighten a hallway with a coat of white paint, and stand at the window watching the sky brighten after a morning of rain.
Brighten goes both ways: you brighten something, or something brightens by itself. It moves from light to mood without changing shape — a face brightens at good news, a phone call brightens a whole grey afternoon, tulips on the table brighten the kitchen. Brighten up is the everyday form: it brightened up after lunch. Careful with the family, though. Bright means clever as well as full of light, but brighten never carries that sense; a good teacher may make a student brighter, and still nobody says she brightened him.
1verbbrightenTo make something lighter or fuller of light, or to become lighter.
“A coat of white paint brightened the whole landing.”
synonyms: lighten
2verbhappierTo make someone happier, or to become more cheerful.
“His face brightened the moment he heard her voice on the phone.”
Too few real examples of this word to estimate which sense is commonest.
Proto-Indo-European
*bʰerHǵ- — to gleam, shine, whiten
Proto-Germanic
*berhtaz — bright
Proto-West Germanic
*berht
Old English
berht
Middle English
bright
English
bright
English, today
brighten
From bright + -en. bright The adjective is from Middle English bright, from Old English berht, beorht, bryht, byrht, from Proto-West Germanic berht, from Proto-Germanic berhtaz (“bright”), ultimately from Proto-Indo-European bʰerHǵ- (“to gleam, shine, whiten”). The noun is derived from Middle English bright (“brightness, brilliance; daylight; light”), from bright: see above. 2
Etymology from Wiktionary, CC BY-SA