threaten

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

• intransitive verb To express a threat against or give indications of taking hostile action against.
• intransitive verb To be a source of danger to; endanger.
• intransitive verb To give signs or warning of; portend.
• intransitive verb To announce the possibility of (something) in a threat or prediction.
• intransitive verb To cause (someone) to feel that his or her power, social standing, or self-esteem is in danger of being diminished.
• intransitive verb To express or use threats.
• intransitive verb To indicate or be a source of danger or harm.

from The Century Dictionary.

• To use threats or menaces; have a menacing aspect.
• To give indication of menace, or of impending danger or mischief; become overcast, as the sky.
• To declare an intention of doing mischief to or of bringing evil on: use threats toward; menace; terrify, or attempt to terrify, by menaces: with with before the evil threatened.
• To charge or enjoin solemnly or with menace.
• To be a menace or source of danger to.
• To give ominous indication of; presage; portend: as, the clouds threaten rain or a storm.
• To announce or hold out as a penalty or punishment: often followed by an infinitive clause.
• Synonyms Menace, Threaten (see menace), forebode, foreshadow.

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

• transitive verb To utter threats against; to menace; to inspire with apprehension; to alarm, or attempt to alarm, as with the promise of something evil or disagreeable; to warn.
• transitive verb To exhibit the appearance of (something evil or unpleasant) as approaching; to indicate as impending; to announce the conditional infliction of.
• intransitive verb To use threats, or menaces; also, to have a threatening appearance.

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

• verb To make a threat against someone; to use threats.
• verb To menace, or be dangerous.
• verb To portend, or give a warning.

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

• verb to be a menacing indication of something:
• verb pose a threat to; present a danger to
• verb to utter intentions of injury or punishment against: