Crossword Genius

No sitter, is ill-at-ease (6)

Ross

I believe the answer is:

uneasy

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'ill-at-ease' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

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(Other definitions for uneasy that I've seen before include "Anxious, nervous" , "as a crowned head, proverbially" , "Restless, perturbed" , "Anxious and unsure, restless" , "Shakespeare: '. . . . . lies the head that wears a crown'" .)

I've seen this clue in the Evening Standard.
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