A short riddle that's unbelievable (2,2)
I believe the answer is:
as if
'unbelievable' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'a short riddle' is the wordplay.
'short' means to remove the last letter.
'riddle' becomes 'sift' (riddle can mean to sieve or sift).
'sift' with its final letter taken off is 'sif'.
'a'+'sif'='AS-IF'
'that's' is the link.
Can you help me to learn more?
(Other definitions for as if that I've seen before include "Expression of incredulity" , "You're joking!" , "Unbelievable!" , "a voice of doubt" , "Yeah right!" .)