taru-adjective, adverb taking the 'to' particle
dejected; dispirited; crestfallen
Literary, somewhat old-fashioned word describing a visible state of dejection or discouragement. Often used with として or たる to modify a noun or verb.
He hung his head dejectedly.
He left the room with a crestfallen look.
lonely and dejected; alone and crestfallen
The kanji 悄 means 'quiet, sad' and 然 is a suffix forming adjectives/adverbs. The reading is on'yomi. The exact historical derivation is uncertain, but the word has been used in literary Japanese to describe a dejected state.