Well acquainted with the metric system (6)

I believe the answer is:

versed

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'well' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I can't see?

I cannot understand how the remainder of the clue works.

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(Other definitions for versed that I've seen before include "Knowing much" , "Accomplished" , "Proficient" , "Experienced or knowledgeable" , "Is well informed" .)

I've seen this clue in The Guardian and The Globe and Mail.

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