Computerised, it's not completely like the real thing (3)
I believe the answer is:
sim
'computerised it's' is the definition.
I can't judge whether this defines the answer.
'not completely like the real thing' is the wordplay.
'not completely' means to remove the last letter (the word is incomplete).
'like' becomes 'sic' (I've seen this before).
'the real thing' becomes 'm' (I can't justify this - if you can you should give a lot more credence to this answer).
'sic' with its final letter removed is 'si'.
'si'+'m'='SIM'
Can you help me to learn more?
(Other definitions for sim that I've seen before include "Role-playing game" , "computer game" , "Card storing data" , "Information carrier" , "Identifying card in a mobile phone" .)