Seen when frowning to be popular (7)

I believe the answer is:

lowbrow

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'seen' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?

I can't explain the rest of the clue.

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(Other definitions for lowbrow that I've seen before include "Person of uncultivated tastes" , "Downmarket" , "Unsophisticated" , "Hard mass in wood, shore bird" , "Unintellectual" .)

I've seen this clue in The Daily Express.

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