be certain

be certain

To be sure (about something); to know definitively (that something will happen or is the case). A: "Yes, Michael's coming tonight." B: "Are you certain? It's already past seven, and he's not here yet." I'm certain that the stove is off—I double-checked it myself.
See also: certain
Farlex Dictionary of Idioms.
See also:
  • certain
  • be certain of (something)
  • certain sure
  • go on the prowl
  • treat (someone or something) like (someone or something else)
  • treat like
  • under certain circumstances
  • (somewhere or something) or bust
  • or bust
  • be a dead cert