Six in court case that's unimportant (7)
I believe the answer is:
trivial
'unimportant' is the definition.
(similar in meaning)
'six in court case' is the wordplay.
'six' becomes 'VI' (Roman numerals).
'in' indicates putting letters inside.
'court case' becomes 'trial' (I've seen this before).
'vi' put within 'trial' is 'TRIVIAL'.
'that's' is the link.
(Other definitions for trivial that I've seen before include "Worthless" , "Rival it, being unimportant" , "Of little importance" , "Trifling" , "Very easy" .)