taru-adjective, adverb taking the 'to' particle
quiet and secluded; tranquil and remote
A literary, somewhat archaic word describing a deeply quiet, isolated, and serene atmosphere, often of a place in nature. Used as a たる adjective or with と adverbially.
The temple deep in the mountains was wrapped in a quiet and secluded stillness.
Mist hung quietly and remotely in the valley bottom.
The exact derivation is uncertain; the kanji 幽 (secluded, deep) and 然 (state, condition) combine to suggest a state of deep quiet and isolation.