threatening

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Making or implying threats.
• adjective Gving warning signs of bad weather.
• adjective Causing the feeling that one's power, social standing, or self-esteem is in danger of being diminished.

from The Century Dictionary.

• noun The act of one who threatens; a threat; a menace; a menacing.
• Indicating or containing a threat or menace.
• Indicating some impending evil; specifically, indicating rain or snow.
• Letters demanding money or other property with menaces.
• Letters threatening to accuse any person of a crime, for the purpose of extorting money.
• Letters threatening to kill a person. The precise definition of what facts constitute a penal offense in this respect varies much with the law in different jurisdictions.
• Synonyms Menacing, minatory.

from the GNU version of the Collaborative International Dictionary of English.

• a. & n. from threaten, v.
• (Law) letters containing threats, especially those designed to extort money, or to obtain other property, by menaces; blackmailing letters.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb Present participle of threaten.
• adjective Presenting a threat; menacing; frightening.
• noun An act of threatening; a threat.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective darkened by clouds
• adjective threatening or foreshadowing evil or tragic developments