Deceptive trick (4)
'deceptive trick' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for hoax that I've seen before include "Fool" , "Prank" , "Imposture" , "Fake, such as Piltdown Man" , "Deliberate trickery" .)
(Other definitions for ruse that I've seen before include "Plan intended to deceive" , "Deceptive manoeuvre" , "Deceptive device" , "trick played" , "Ploy, artifice" .)