Boast pay can secure plant (8)
I believe the answer is:
crowfoot
'plant' is the definition.
(crowfoot is a kind of plant)
'boast pay' is the wordplay.
'boast' becomes 'crow' (crowing is a kind of boasting).
'pay' becomes 'foot' (as in footing the bill).
'crow'+'foot'='CROWFOOT'
'can secure' is the link.
(Other definitions for crowfoot that I've seen before include "flower" , "Aquatic plant related to buttercup" .)