also: せきとした
noun-modifying (irregular)
Describes a scene or atmosphere that is deeply quiet and still, often with a slightly literary or formal tone. Used prenominally (before a noun).
寂とした森の中を歩いた。
I walked through the still, hushed forest.
夜の寺は寂とした空気に包まれていた。
The temple at night was wrapped in a hushed atmosphere.
静か is the common word for 'quiet' and can be used in everyday speech. 寂とした is more literary and emphasizes a profound, almost solemn stillness.
ひっそり is an adverb meaning 'quietly' or 'secretly', often implying a lack of people or activity. 寂とした focuses on the atmosphere of stillness itself.
From the kanji 寂 (stillness, loneliness) combined with the classical copula と and the past/perfective form した of する, forming a fixed prenominal expression.