To tantalise the left is a plant (6)
I believe the answer is:
Here is my best explanation:
'a plant' is the definition.
(teasel is a kind of plant)
'to tantalise the left' is the subsidiary indication.
'to tantalise' becomes 'tease' (teasing is a kind of tantalizing).
'the left' becomes 'l' (common abbreviation).
'is' is the link.
(Other definitions for teasel that I've seen before include "Elates with nap-brushing device", "Sat eel up on the herb", "Eel sat up on the plant", "Plant with prickly flower heads", "Herb with prickly flower heads -- elates (anag)", "Plant with prickly flower head", "Prickly plant - elates (anag)", "Plant with spiny purple flower heads", "Prickly plant (S, not Z)" and "Prickly wild plant".)