taru-adjective, adverb taking the 'to' particle
suddenly; abruptly; unexpectedly
Literary or formal adverb describing something happening all at once, often with a dramatic or surprising nuance. Commonly used with と (忽然と).
He suddenly vanished.
Suddenly, a fog rolled in.
Standard kanji spelling.
Mixed kanji-kana spelling; less common but still encountered.
The kanji 忽 (こつ) means 'suddenly' or 'neglect', and 然 (ぜん) is a suffix forming adverbs. The exact historical derivation is uncertain, but the compound is used in classical Chinese and literary Japanese.