Prickly plant beginning to tickle one under canvas (6)
I believe the answer is:
teasel
'prickly plant' is the definition.
(I've seen this before)
'beginning to tickle one under canvas' is the wordplay.
I cannot quite see how this works, but
'tickle' could be 'tease' and 'tease' is found in the answer.
A single letter 'l' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for teasel that I've seen before include "Elates with nap-brushing device" , "Spiny flower head" , "Plant with prickly flower heads" , "Tall prickly plant" , "Prickly plant (S, not Z)" .)