Stimulating mixture of gin in taxi to start carousing (12)
I believe the answer is:
intoxicating
'stimulating' is the definition.
(intoxicating is a kind of stimulating)
'mixture of gin in taxi to start carousing' is the wordplay.
'mixture of' indicates an anagram (I've seen this in other clues).
'start' indicates taking the first letters.
The initial letter of 'carousing' is 'c'.
'gin'+'in'+'taxi'+'to'+'c'='ginintaxitoc'
'ginintaxitoc' with letters rearranged gives 'INTOXICATING'.
(Other definitions for intoxicating that I've seen before include "Exciting, exhilarating" , "Making drunk" .)