Astonished to forget when building top of cement mixer (5)
I believe the answer is:
tonic
'mixer' is the definition.
(I've seen this before)
'astonished to forget when building top of cement' is the wordplay.
I cannot really understand how this works, but
'to' is present in the answer.
The remaining letters 'nic' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for tonic that I've seen before include "Restorative that invigorates" , "something nice and fresh" , "__water; gin mixer" , "do for musicians" , "Invigorating medicine - keynote" .)