Threaten

I can't think of any that it would cover all  cases.  This is a tough verb.

--------- 

threat·en

 transitive verb
1 : to utter threats against : promise punishment, reprisal, or other distress to <threaten trespassers with arrest>
2 archaic : to charge under pain of punishment : WARN <let us straitly threaten them, that they speak henceforth to no man in this name -- Acts 4:17 (Authorized Version)>
3 : to promise as a threat : hold out by way of menace or warning <threaten punishment to all trespassers>
4 a : to give signs of the approach of (something evil or unpleasant) : indicate as impending : PORTEND <the sky threatens storm> b : to hang over as a threat : MENACE <famine threatens the city>
5 : to announce as intended or possible <threaten to buy a car>

intransitive verb
1 : to utter or use threats or menaces
2 : to have a menacing appearance : portend evil

 http://unabridged.merriam-webster.com

-------- 

Liveinjapan

I think the definition 'to utter' makes me comfortable. 

Hmmm. I don't personally see why it makes any difference if it's an utterance or not. I don't see why "it's threatening to happen" (not an utterance) and "he's threatening to leave" (probably an utterance) should be any different in terms of "transitiveness".

Edit (later addition): 

Liveinjapan

It looks like, in the first, "him" is omitted after "threatened."

Although it would accord with the general meaning, there is, syntactically, no implied-but-omitted "him". Certainly not to me, anyway.