Running inspection, a sample (4,2,5)
I believe the answer is:
case in point
'sample' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'running inspection a' is the wordplay.
'running' indicates an anagram.
'inspection'+'a'='inspectiona'
'inspectiona' anagrammed gives 'CASE IN POINT'.
Can you help me to learn more?
(Other definitions for case in point that I've seen before include "Particular example" , "Example of what is under discussion" .)