Brainiac originally getting stuck into a large, complex calculation (7)
I believe the answer is:
algebra
'calculation' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'brainiac originally getting stuck into a large complex' is the wordplay.
'originally' says to take the initial letters.
'getting stuck into' is an insertion indicator.
'complex' indicates an anagram.
The first letter of 'brainiac' is 'b'.
'a'+'large'='alarge'
'alarge' is an anagram of 'algera'.
'b' put within 'algera' is 'ALGEBRA'.
Can you help me to learn more?
(Other definitions for algebra that I've seen before include "Form of maths" , "Branch of generalised arithmetic" , "Symbol-based branch of mathematics" , "Symbolic maths" , "letters here set out the problem" .)