Spike of the willow (6)
I believe the answer is:
catkin
'spike of the willow' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for catkin that I've seen before include "Willow or hazel flower spike" , "Flowering shoot of willow etc" , "Lamb's-tail, e.g." , "Kit can (anag.)" , "Feature of willow/hazel" .)