Thus, at opening time, he fancies a drink (3)
I believe the answer is:
sot
'he fancies a drink' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'thus at opening time' is the wordplay.
'thus' becomes 'so' (synonyms).
'at opening' indicates taking the first letters.
The initial letter of 'time' is 't'.
'so'+'t'='SOT'
Can you help me to learn more?
(Other definitions for sot that I've seen before include "A chronic drinker" , "Habitual drinker" , "Boozer" , "Lush" , "Habitual drunkard" .)