Strangely, he dreamt that he drank with a dormouse (3,3,6)
I believe the answer is:
the mad hatter
'he drank with a dormouse' is the definition.
The definition suggests a singular noun which matches the answer.
'strangely he dreamt that' is the wordplay.
'strangely' indicates anagramming the letters.
'hedreamtthat' anagrammed gives 'THE MAD HATTER'.
Can you help me to learn more?
(Another definition for the mad hatter that I've seen is " party member".)