1 make a threat or threats against.
2 be a sign or indication of (something undesirable).
3 (foll. by to + infin.) announce one's intention to do an undesirable or unexpected thing (threatened to resign).
4 (also absol.) give warning of the infliction of (harm etc.) (the clouds were threatening rain).
Derivatives:
threatener n. threateningly adv.
Etymology: OE threatnian (as THREAT)
Useful english dictionary. 2012.