Cast dumbfounded (6)
I believe the answer is:
thrown
This clue could be a double definition.
'cast' is the first definition.
(I've seen this before)
'dumbfounded' is the second definition.
The answer and definition can be both related to thinking as well as being past participle verbs.
Perhaps there's a link between them I don't understand?
Can you help me to learn more?
(Other definitions for thrown that I've seen before include "Confused; chucked" , "given up intentionally" , "Confused - cast" , "Disconcerted; chucked" , "Unsettled" .)