Visitor made an estimation in report (5)
I believe the answer is:
guest
'visitor' is the definition.
(someone visiting a place)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for guest that I've seen before include "Someone invited" , "Conjectured audibly" , "Visitor, lodger" , "One who's invited" , "Person entertained by host" .)