Warning of reduced activity? (6)
I believe the answer is:
'warning' is the definition.
(I know that lesson is a type of warning)
'reduced activity?' is the wordplay.
'reduced' becomes 'less' (a reduced amount).
'activity?' becomes 'on' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for lesson that I've seen before include "Teaching unit" , "See 1" , "corrective punishment" , "Sermon or class session" , "Unit of instruction" .)