MINACIOUS
baleful, forbidding, menacing, minacious, minatory, ominous, sinister, threatening
(adjective) threatening or foreshadowing evil or tragic developments; “a baleful look”; “forbidding thunderclouds”; “his tone became menacing”; “ominous rumblings of discontent”; “sinister storm clouds”; “a sinister smile”; “his threatening behavior”; “ugly black clouds”; “the situation became ugly”
Source: WordNet® 3.1
Etymology
Adjective
minacious (not comparable)
(now rare) Threatening, menacing.
Source: Wiktionary
Mi*na"cious, a. Etym: [L. minax, -acis. See Menace.]
Definition: Threatening; menacing. [R.]
Source: Webster’s Unabridged Dictionary 1913 Edition