Case is plain with ivory top inlaid (7)

I believe the answer is:

patient

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'case' is the definition.
(a medical case)

I don't understand the remainder of the clue.

(Other definitions for patient that I've seen before include "one of interest to medics?" , "Willing to wait" , "one receiving medical treatment" , "convalescent" , "Unhurried" .)

I've seen this clue in The Guardian.

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