Webster's Revised Unabridged Dictionary · 1913

Tenebrous

Tenebrous , adjective

[Latin tenebrosus, from tenebrae darkness: compare French ténébreux.]

Dark; gloomy; dusky; tenebrious.
The most dark, tenebrous night. — J. Hall (1565)
The towering and tenebrous boughts of the cypress. — Longfellow