Change into certain reciprocal movement (11)

I believe the answer is:

interaction

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'reciprocal movement' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'change into certain' is the wordplay.
'change' is an anagram indicator.
'into'+'certain'='intocertain'
'intocertain' anagrammed gives 'INTERACTION'.

Can you help me to learn more?

(Other definitions for interaction that I've seen before include "Reciprocal influence" , "which works two ways" .)

I've seen this clue in The Irish Independent.

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