Tequila source (5)
I believe the answer is:
agave
'tequila source' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for agave that I've seen before include "source of tequila" , "Spiky succulent" , "Succulent; daughter of Cadmus" , "Plant, source of sisal" , "plant in Mexico" .)