guesstimate
Concise Oxford English Dictionary © 2008 Oxford University Press:
guesstimate (also guestimate) informal
▶noun /ˈgɛstɪmət/ an estimate based on a mixture of guesswork and calculation. ▶verb /ˈgɛstɪmeɪt/ form a guesstimate of.
'guesstimate' also found in these Oxford entries:

