See there's a knack in standing upright (8)

I believe the answer is:

straight

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'upright' is the definition.
(synonyms)

I can't explain the rest of the clue.

(Other definitions for straight that I've seen before include "In a direct line" , "Serious" , "Without deviation" , "(Of drink) undiluted" , "Without deviations or curves" .)

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