Article one’s involved in writing up (5)
I believe the answer is:
amiss
'up' is the definition.
(thesaurus)
'article one's involved in writing' is the wordplay.
'article' becomes 'a' (indefinite article).
'one's' becomes 'is' (roman numeral**).
'involved in' means one lot of letters goes inside another.
'writing' becomes 'ms' (abbreviation for manuscript).
'is' inserted inside 'ms' is 'miss'.
'a'+'miss'='AMISS'
(Other definitions for amiss that I've seen before include "Haywire" , "Unsuitable" , "Mistakenly" , "Wrongly" , "Not functioning properly" .)