Printing mistake, rare, unsettled corporation (7)
I believe the answer is:
erratum
'printing mistake' is the definition.
(an erratum is a typographical error)
'rare unsettled corporation' is the wordplay.
'unsettled' is an anagram indicator.
'corporation' becomes 'tum' (I've seen this before).
'rare' anagrammed gives 'erra'.
'erra'+'tum'='ERRATUM'
(Other definitions for erratum that I've seen before include "fluff on paper" , "something wrong?" , "Faux pas" , "Mistake in book, etc" , "Typo" .)