Senate's leader almost uncovered treacherous person (5)
I believe the answer is:
snake
'treacherous person' is the definition.
(I've seen this in another clue)
'senate's leader almost uncovered' is the wordplay.
'leader' says to take the initial letters.
'almost' means to remove the last letter (most of the word but not all of it).
'uncovered' becomes 'naked' (I've seen this in another clue).
The first letter of 'senates' is 's'.
'naked' with its final letter removed is 'nake'.
's'+'nake'='SNAKE'
(Other definitions for snake that I've seen before include "former EC currency band" , "Long slender reptile" , "Serpent" , "Slithering reptile" , "Chinese zodiac animal" .)