Spike of frozen water (6)
I believe the answer is:
icicle
'spike of frozen water' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for icicle that I've seen before include "point of cold water" , "Frozen water drip" , "Pendent spear of frozen water" , "Hanging piece of frozen liquid" , "this tapers" .)