Deceit admitted by a new immigrant (5)
I believe the answer is:
'immigrant' is the definition.
(I've seen this before)
'deceit admitted by a new' is the wordplay.
'deceit' becomes 'lie' (I've seen this in other clues).
'admitted by' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'lie' going within 'an' is 'ALIEN'.
(Other definitions for alien that I've seen before include "of foreigners" , "Belonging to a foreign country" , "exciting film based in space" , "Foreign; extraterrestrial" , "Not native" .)