Minor, four, appearing in a court case (7)
I believe the answer is:
trivial
'minor' is the definition.
(thesaurus)
'four appearing in a court case' is the wordplay.
'four' becomes 'iv' (roman numeral).
'appearing in' means one lot of letters goes inside another.
'a court case' becomes 'trial' (I've seen this before).
'iv' placed within 'trial' is 'TRIVIAL'.
(Other definitions for trivial that I've seen before include "Of little importance" , "Frivolous" , "not significant" , "lacking weight" , "Footling" .)