adverb, adverb taking the 'to' particle
with a momentary flash; glint; sparkle
Mimetic adverb describing a brief, sharp flash or glint of light, often used with と or as a standalone adverbial.
彼の目がきらりと光った。
His eyes flashed for an instant.
星がきらりと輝いた。
A star twinkled brightly.
Mimetic word derived from the sound or sensation of a quick flash of light. The exact origin is uncertain.