1. 
[syn: baleful, forbidding, menacing, minacious, minatory, ominous, sinister, threatening]
The Collaborative International Dictionary of English v.0.48:
Minacious \Mi*na"cious\, a. [L. minax, -acis. See Menace.]
   Threatening; menacing. [R.]
   [1913 Webster]
WordNet (r) 3.0 (2006):
minacious
    adj 1: 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" [syn: baleful, forbidding,
           menacing, minacious, minatory, ominous,
           sinister, threatening]