taru-adjective, adverb taking the 'to' particle
brilliantly shining; glittering
Literary or poetic word describing light that shines brilliantly or glitteringly. Used as a taru-adjective or adverb with と. Rare in modern everyday speech.
The stars were glittering brilliantly in the night sky.
Her eyes were shining brilliantly, just like jewels.
Alternate kanji spelling without iteration mark. Both kanji forms are rare; the word is mostly encountered in literary contexts.
Reduplication of the kanji 輝 (ki, 'shine'), forming a literary adjective/adverb. The exact historical derivation is uncertain, but it follows a pattern of reduplicated kanji compounds used in classical Japanese.