Class teacher initially involved in court action (5)
I believe the answer is:
caste
'class' is the definition.
(caste is a kind of class)
'teacher initially involved in court action' is the wordplay.
'initially' suggests taking the first letters.
'involved in' indicates putting letters inside.
'court action' becomes 'case' (as in a court case).
The initial letter of 'teacher' is 't'.
't' put inside 'case' is 'CASTE'.
(Other definitions for caste that I've seen before include "Social division in Hinduism" , "Social status" , "Large, long-necked, wading bird" , "Hereditary Hindu social division" , "Social class in Hinduism" .)