I guess not

I guess not

An expression of vague denial or negation. A: "Is Tom coming?" B: "I guess not—it's getting pretty late."
See also: guess, not
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

I guess not.

 and (I) don't think so.; I expect not.; I suppose not.; I suspect not.; I think not.
a vague statement of negation. (More polite or gentle than simply saying no. Frequently, in speech, suppose is reduced to 'spose, and expect and suspect are reduced to 'spect. The apostrophe is not always shown.) Bill: It's almost too late to go to the movie. Shall we try anyway? Mary: I guess not. Tom: Will it rain? Mary: I 'spect not.
See also: guess, not
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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