Peak movement's launch at union assembly (8)

I believe the answer is:

mountain

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'peak' is the definition.
(mountain peak is a kind of peak)

'movement's launch at union assembly' is the wordplay.
'movement's launch' becomes 'm' (I can't explain this - if you can you should believe this answer much more).
'assembly' is an anagram indicator.
'at'+'union'='atunion'
'atunion' with letters rearranged gives 'ountain'.
'm'+'ountain'='MOUNTAIN'

Can you help me to learn more?

(Other definitions for mountain that I've seen before include "high position" , "Alp" , "Natural elevation of the earth's surface" , "Two-wheeler designed for rough terrain" , "eg Everest" .)

I've seen this clue in the Sydney Morning Herald.

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