See tsar perhaps cut by old upper-class — tough (9)
I believe the answer is:
laborious
'see tsar perhaps cut by old upper-class tough' is the definition.
I can't judge whether this definition defines the answer.
'class tough' is the wordplay.
'class' becomes 'labor' (labor is a kind of class).
'tough' becomes 'ious' (I can't justify this - if you can you should give a lot more credence to this answer).
'labor'+'ious'='LABORIOUS'
Can you help me to learn more?
(Other definitions for laborious that I've seen before include "Gruelling" , "Using much time and effort" , "Tedious" , "Requiring considerable time and effort" , "Arduous" .)