Once more taken aback for 1 say (5)
I believe the answer is:
taser
'1 say' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'once more taken aback' is the wordplay.
'once more' becomes 're' (prefix in words like 're-emerge' or 're-enter').
'taken' becomes 'sat' (sit can mean to take an exam).
'aback' says the letters should be written in reverse.
're'+'sat'='resat'
'resat' back-to-front is 'TASER'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for taser that I've seen before include "shocker" , "Shocking device used by the police?" , "A shocking thing" , "Electrical weapon" , "Gun firing electrified barbs" .)