Not the complete sleuth (3)
I believe the answer is:
tec
'sleuth' is the definition.
(short for detective)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tec that I've seen before include "Busy" , "CID officer (abbrev.)" , "Detective (colloq.)" , "Investigator" .)