Caller copying Doctor Celsius mixed big drink (11)
I believe the answer is:
mockingbird
'caller copying' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'doctor celsius mixed big drink' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'celsius' becomes 'c' (synonyms).
'mixed' is an anagram indicator.
'big'+'drink'='bigdrink'
'bigdrink' is an anagram of 'kingbird'.
'mo'+'c'+'kingbird'='MOCKINGBIRD'
Can you help me to learn more?
(Other definitions for mockingbird that I've seen before include "American avian mimic" , "American mimic of the thrush family" , "winger" , "American songbird" , "Avian mimic (don't kill it!)" .)