Short answer about deception and little green men (6)
I believe the answer is:
aliens
'little green men' is the definition.
(I've seen this in another clue)
'short answer about deception' is the wordplay.
'short answer' becomes 'ans' (abbreviation for answer; 'short' suggests an abbreviation).
'about' is an insertion indicator.
'deception' becomes 'lie' (lying to someone is deceiving them).
'ans' going around 'lie' is 'ALIENS'.
'and' acts as a link.
(Other definitions for aliens that I've seen before include "Foreigners or creatures from outer space" , "Outsiders" , "Immigrants" , "Strange forms of life" , "Strangers, extraterrestrials" .)