Glucose containing leaves (3)
I believe the answer is:
cos
'leaves' is the definition.
Although both the answer and definition are plural nouns, I can't see how they can define each other.
'glucose containing' is the wordplay.
'containing' indicates the answer is hidden within the clue (I've seen 'contains' mean this).
'COS' is hidden within 'glucose'.
Can you help me to learn more?
(Other definitions for cos that I've seen before include "Salad ingredient" , "Casual as" , "Mozart fidelity-test opera" , "often associated with sin" , "Island in Mediterranean" .)