Tread lightly (6)
I believe the answer is:
tiptoe
'tread lightly' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tiptoe that I've seen before include "Lightly pad" , "Walk quietly on the balls of one's feet" , "or get a bit higher on this?" , "go quietly" , "Go carefully" .)