A botanist's angle? (4)
I believe the answer is:
'a botanist's angle?' is the definition.
(I've seen this in another clue)
'a botanist's angle?' is the wordplay.
'botanist' becomes 'xi' (I can't justify this - if you can you should believe this answer much more).
'angle?' becomes 'l'.
Can you help me to learn more?
(Another definition for axil that I've seen is " Angle between leaf and stem".)