1) American slang 2) Approximation 3) Ballpark figure 4) Conjecture 5) Estimate 6) Estimation 7) Guestimate 8) Idea 9) Number in the ball park 10) To make a guesstimate 1) Approximation 2) Guestimate 3) Stab 
Guesstimate is an informal English portmanteau of guess and estimate, first used by American statisticians in 1934 or 1935. It is defined as an estimate made without using adequate or complete information, or, more strongly, as an estimate arrived at by guesswork or conjecture. Like the words estimate and guess, guesstimate may be used as a verb o...
[n] - an estimate that combines reasoning with guessing 2. [v] - estimate based on a calculation
guestimate noun an estimate that combines reasoning with guessing