noun, taru-adjective, adverb taking the 'to' particle
sorrowfully; with a heavy heart
Archaic/literary word describing a deeply sorrowful or melancholy state. Often used in classical or highly formal written contexts. The 'taru' adjective and 'to' adverb forms are typical of classical Japanese grammar.
愁然として、彼は故郷を後にした。
Sorrowfully, he left his hometown behind.
愁然たる面持ちで、彼女は窓の外を眺めていた。
With a sorrowful expression, she was gazing out the window.