Addict in deception, right to the end (4)
I believe the answer is:
user
'addict' is the definition.
(drug user)
'deception right to the end' is the wordplay.
'deception' becomes 'us' (I can't explain this - if you can you should believe this answer much more).
'right' becomes 'r' (common abbreviation).
'to' means one lot of letters go next to another (I've seen this in other clues).
'end' says to take the final letters.
The final letter of 'the' is 'e'.
'r' after 'e' is 'er'.
'us'+'er'='USER'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for user that I've seen before include "Person taking drugs" , "Manipulative woman" , "One exploiting others" , "One taking drugs" , "Ruse for employer" .)