'guesstimate' definitions:

Definition of 'guesstimate'

(from WordNet)
noun
An estimate that combines reasoning with guessing [syn: guesstimate, guestimate]
verb
Estimate based on a calculation

Definition of 'guesstimate'

From: GCIDE
  • guesstimate \guess"ti*mate\ n. [from guess and estimate] an estimate based on little information, being little better than a guess. [PJC]