Detectives receiving boost, source of a big shift (9)
I believe the answer is:
tectonics
'source of a big shift' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Maybe there's an association between them I don't understand?
'detectives receiving boost' is the wordplay.
'detectives' becomes 'tecs' ('tec' can be a synonym of 'detective').
'receiving' means one lot of letters goes inside another.
'boost' becomes 'tonic' (tonic can mean a stimulant or booster).
'tecs' placed around 'tonic' is 'TECTONICS'.
Can you help me to learn more?
(Other definitions for tectonics that I've seen before include "Structural geology" , "Processes in the earth's crust" , "scientific study of buildings" , "Moving plates" .)