I think not

I think not

An expression of vague denial or negation. A: "Is Tom coming?" B: "I think not—it's getting pretty late."
See also: not, think
Farlex Dictionary of Idioms.
See also:
  • not in a million years
  • not in a month of Sundays
  • think to (do something)
  • think to do
  • I think so
  • never in a month of Sundays
  • never in a million years
  • (someone) thinks (they) are so smart
  • think back
  • go against the flow