Thinking aiming was off, having swallowed some alcohol (9)
I believe the answer is:
imagining
'thinking' is the definition.
('imagine' can be a synonym of 'think')
'aiming was off having swallowed some alcohol' is the wordplay.
I cannot quite see how this works, but
an anagram of 'aiming' is 'imagin' which is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for imagining that I've seen before include "Supposing, assuming" , "Fantasising" , "illusion?" , "Fancying" , "Thinking up" .)