Between a couple, the tango is very important (5)

I believe the answer is:

vital

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'is very important' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

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(Other definitions for vital that I've seen before include "Essential to life, indispensable" , "Critical, necessary" , "Essential for life; key" , "Spirited" , "Of key importance" .)

I've seen this clue in the Evening Standard.

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