Assumed South Africa used in film Zulu (6)

I believe the answer is:

ersatz

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'assumed' is the definition.
(thesaurus)

'south africa used in film zulu' is the wordplay.
'south africa' becomes 'rsa' (I can't explain this - if you can you should give a lot more credence to this answer).
'used in' indicates putting letters inside.
'film' becomes 'ET' (E.T. the Extra-Terrestrial).
'zulu' becomes 'Z' (phonetic alphabet: alpha, bravo, charlie etc.).
'rsa' placed within 'et' is 'ersat'.
'ersat'+'z'='ERSATZ'

Can you help me to learn more?

(Other definitions for ersatz that I've seen before include "Mock" , "inferior type" , "Made in imitation, from German" , "unnatural" , "Inferior substitute" .)

I've seen this clue in The Telegraph.

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