adverb taking the 'to' particle, taru-adjective
Literary or classical expression describing a cheerful, pleasant state of mind. Often used with として or たる in formal writing.
彼は快然として日々を過ごしている。
He spends his days in a cheerful and contented manner.
na-adjective
cured; recovered from illness
Rare, literary use for recovery from sickness. Modern Japanese would more commonly use 治る or 回復する.
病が快然となった。
The illness has been cured. (literary)