Argument with sibling after tea in Paris (6)
I believe the answer is:
thesis
'argument' is the definition.
(a thesis is an argument or proposal)
'sibling after tea in paris' is the wordplay.
'sibling' becomes 'sis' (short for sister).
'after' means one lot of letters go next to another.
'tea in paris' becomes 'the' ('tea' in French).
'sis' put after 'the' is 'THESIS'.
'with' is the link.
(Other definitions for thesis that I've seen before include "Dissertation presented for a doctorate" , "research paper" , "Long research essay or treatise written for university degree" , "Proposition" , "Essay putting forward a particular view" .)