Series of announcements in Oz (5)

I believe the answer is:

ounce

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'series of announcements in oz' is the definition.
'ounce' can be an answer for 'oz' (I've seen this before). I'm unsure of the 'series of announcements in' bit.

'of announcements in oz' is the wordplay.
'of' becomes 'o'.
'announcements in oz' becomes 'unce' (I can't explain this - if you can you should believe this answer much more).
'o'+'unce'='OUNCE'

Can you help me to learn more?

(Other definitions for ounce that I've seen before include "Wildcat" , "one of several in a pound" , "prowler" , "Unit equal to about 28 grams" , "Enough to tip the scales" .)

I've seen this clue in The Independent.

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