Superlatively stupid, however for Texan (9)

I believe the answer is:

leastwise

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'superlatively' is the definition.
Both the definition and answer are adverbs.
Maybe they are linked in a way I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for leastwise that I've seen before include "infrequently occurring" , "in Hollywood at any rate" , "anyway" , "If nothing else" , "However (US)" .)

I've seen this clue in The Times.

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