Colourless liquid (5)
I believe the answer is:
water
'colourless liquid' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for water that I've seen before include "Superior's full of it" , "It's to be found in puddles, pools and ponds" , "What makes the Somme" , "Essential liquid" , "Commonest fluid" .)