Synonyms for Happen:

n.

turn up, unfold. come around, recur, spring, repeat, turn out, come off, arrive, result, issue, appear. tumble on, bump into, meet up with. happen (noun)
encounter, hap, come about, take place, go on, chance, occur, pass off, bump, find, pass.

v.

come to pass; occur (verb)
chance, go on, ensue, spring, eventuate, come off, take place, transpire, pass, follow, develop, arise, result, turn up, issue, turn out, befall, come about, appear, bump, arrive, recur.
happen (verb)
come to pass, pass, take place.
occur (verb)
eventuate, occur, ensue, follow, befall, transpire, develop, arise.

Other synonyms:

repeat, unfold. come off. come off
take place.
return
recur.
Other relevant words:
come about, find, turn up, unfold, arrive, hap, bump, result, pass off, appear, chance, go on, recur, spring, come off, issue, encounter.

Usage examples for happen

  1. Anything happen to you? – The Boy Scout Aviators by George Durston
  2. You wouldn't believe it, would you, but I know, and it didn't happen so long ago either. – The Man Who Knew by Edgar Wallace
  3. But what will happen to him? – A Diary Without Dates by Enid Bagnold