First witness to take stand was treacherously deceitful (6)
I believe the answer is:
weasel
'treacherously deceitful' is the definition.
I can't judge whether this defines the answer.
'first witness to take stand' is the wordplay.
'first witness' becomes 'w' (est letter of 'witness').
'to take' says to put letters next to each other.
'stand' becomes 'easel' (stand for an artist's canvas).
'w'+'easel'='WEASEL'
'was' is the link.
Can you help me to learn more?
(Other definitions for weasel that I've seen before include "E Wales (anag.)" , "Carnivorous mammal; treacherous person" , "These animal words are intentionally misleading" , "These sort of words are meaningless" , "Sly type" .)