Lesson I arranged for Leo's mate (7)
I believe the answer is:
lioness
'leo's mate' is the definition.
(leo is Latin for 'lion')
'lesson i arranged' is the wordplay.
'arranged' indicates anagramming the letters.
'lesson'+'i'='lessoni'
'lessoni' is an anagram of 'LIONESS'.
'for' acts as a link.
(Other definitions for lioness that I've seen before include "Large cat" , "Big beast's mate" , "Brave woman" , "Leo's mate" , "Female pride member" .)