A Parisian brought up a couple of lines without significance (4)
I believe the answer is:
null
'without significance' is the definition.
(I've seen this in another clue)
'a parisian brought up a couple of lines' is the wordplay.
'a parisian' becomes 'un' ('a' in French).
'brought up' shows that the letters should be reversed in order (in a down clue, letters go up).
'a couple of lines' becomes 'll' (two abbreviations for line).
'un' backwards is 'nu'.
'nu'+'ll'='NULL'
(Other definitions for null that I've seen before include "Lacking any legally binding force" , "Having the value zero -- void" , "Not valid" , "Without legal force" , "Without value or consequence" .)