(idiomatic) I don't know; I have no idea.

(informal) An estimate that is hardly any better than a guess, often because it is based on insufficient or unreliable data.

(intransitive) To make a guesstimate. / (transitive) To make a guesstimate of a specific quantity.

An estimate, judgment or opinion made by guessing, from limited information.

plural of guesstimate

A person who guesses; especially someone who can make a reasonable prediction from little evidence.

plural of guesser

(derogatory) An estimation made without good justification and often biased. / Estimation based on guesses, usually for expedience or because no better method is available.

plural of guesstimation

present participle of guesstimate