Proposition me with other design (7)
I believe the answer is:
theorem
'proposition' is the definition.
(I know that theorem is a type of proposition)
'me with other design' is the wordplay.
'with' means one lot of letters go next to another.
'design' indicates anagramming the letters.
'me' after 'other' is 'otherme'.
'otherme' with letters rearranged gives 'THEOREM'.
(Other definitions for theorem that I've seen before include "Geometrical proposition to be proved" , "Formula to be proved" , "Deduced formula" , "Mathematical formula" , "Proposition not self-evident but proved by a chain of reasoning" .)