Important lesson — change sides (7)

I believe the answer is:

seminal

'important' is the definition.
(seminal can mean important or influential)

I cannot understand how the rest of the clue works.

(Other definitions for seminal that I've seen before include "Of seed, or giving rise to new developments" , "Of beginnings or early developments" , "Germinal" , "Strongly influential" , "Generating new developments for menials" .)

I've seen this clue in The Guardian.

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