Missile base and plant (9)
I believe the answer is:
arrowroot
'plant' is the definition.
(arrowroot is a kind of plant)
'missile base' is the wordplay.
'missile' becomes 'arrow' (arrow is a kind of missile).
'base' becomes 'root' ('root' can be a synonym of 'base'**).
'arrow'+'root'='ARROWROOT'
'and' acts as a link.
(Other definitions for arrowroot that I've seen before include "Starchy plant" , "Medicinal plant" , "Nutritious starch from a West Indian plant" , "that thickens" , "Fine cooking powder" .)