Such an argument can be inadvisable if baseless (7)

I believe the answer is:

invalid

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'such' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I can't see?

I cannot understand how the rest of the clue works.

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(Other definitions for invalid that I've seen before include "Not telling" , "Void; patient" , "Null and void" , "Unsound; ill person" , "Nugatory" .)

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

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