Visitor had an idea, we hear (5)
I believe the answer is:
guest
'visitor' is the definition.
(someone visiting a place)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for guest that I've seen before include "Visitor, lodger" , "Someone invited" , "Caller" , "Visitant" , "Conjectured audibly" .)