See Isaac so confused, missing a dance (9)

I believe the answer is:

ecossaise

I'm a little stuck... Click here to teach me more about this clue!

'dance' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Another definition for ecossaise that I've seen is " Country dance".)

I've seen this clue in The Times.

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