Underhanded tell-tale (5)
I believe the answer is:
sneak
'underhanded tell-tale' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sneak that I've seen before include "thief" , "peach" , "Creep" , "Go furtively and tell tales" , "Telltale; furtive person" .)