Other forms: twinkling, twinkles
To twinkle is to shine with a light that keeps changing. Stars twinkle, twinkling lights, her eyes twinkled.
Stars twinkle because their light passes through moving layers of atmosphere, which is why planets, being discs rather than points, mostly do not — that is the standard way of telling them apart. Of eyes it means shining with amusement. Note twinkling, and in the twinkling of an eye, meaning instantly; and Twinkle Twinkle Little Star, which is set to the same tune as the alphabet song.
1verbtwinkleTo shine with a light that keeps changing.
“The lights of the town twinkled below us as we drove down the hill.”
2verbamusementTo shine with amusement, of the eyes.
“His eyes twinkled and nobody trusted him after that.”
twinkle is a flickering shine.
Old English twinclian is related to twinkle's cousin twitch, from a root about quick movement. The word describes the flicker rather than the light, which is exactly what the physics says.
Old English
twinclian — to twinkle
Middle English
twinclen
English, today
twinkle
From Middle English twinclen, twynclen, from Old English twinclian (“to twinkle”), equivalent to twink + le. Compare German zwinkern (“to wink; twinkle”).
Etymology from Wiktionary, CC BY-SA