Synonyms for Threaten:

n.

advance, inhibit, throttle, disadvantage, overcome, count against, hold back, come-on, approach, seize, loom, embarrass, let down, bring up against, burden, happen, plague. hector, strong-arm, over, bullyrag, show your teeth, bludgeon, cow. safety. foresight. lower, brew, near, overhang, hang over, impend. threaten (noun)
jeopardise, endanger, jeopardize, menace, peril, imperil.

v.

endanger (verb)
menace, hang over, jeopardize, imperil, advance, impend, approach, warn, endanger, risk, loom, frighten, overhang.
frighten (verb)
horrify, haunt, rattle, petrify, harrow, terrify, panic, unnerve, agitate, set on edge, disturb.
threaten (verb)
intimidate, Forewarn, harass, frighten, admonish, forebode, browbeat, warn, bulldoze, torment, hint, bully, scare.
warn (verb)
alarm, advise, caution, alert.
warn, pressure (verb)
browbeat, forebode, abuse, intimidate, caution, cow, fulminate, bully, torment, terrorize, scare, Forewarn, menace, admonish, bluster.

Other synonyms:

bludgeon, lie ahead, impend. lurk, strong-arm, call for, cow, hold over, hector, await, brew, bullyrag, fulminate. loom, overhang. lower. approach
impend.
coerce
terrorize.
endanger
jeopardize.
Other relevant words:
bluster, jeopardise, brew, cow, bullyrag, overhang, near, disadvantage, impend, hector, advance, lie ahead, abuse, peril, fulminate, loom, terrorize, approach, hang over, strong-arm, bludgeon, await, lower.

Usage examples for threaten

  1. As you have been so frank as to- I won't say threaten perhaps warn is the better word- as you have been so good as to warn me, I may, before we part, just give you a word of caution. – From Whose Bourne by Robert Barr
  2. But she alone seemed to watch over the fortunes of her followers; for no other eye could be seen, looking out on the danger that began so seriously to threaten them, both from the heavens, and from a more certain and intelligible, foe. – The Water-Witch or, The Skimmer of the Seas by James Fenimore Cooper