Proposition from me to her (7)
I believe the answer is:
theorem
'proposition' is the definition.
(I know that theorem is a type of proposition)
'from me to her' is the wordplay.
'from' is an anagram indicator (from the letters).
'me'+'to'+'her'='metoher'
'metoher' anagrammed gives 'THEOREM'.
(Other definitions for theorem that I've seen before include "deduction" , "(Maths) proposition" , "Proven proposition" , "Mathematical axiom" , "Hero met (anag) - principle that's proven" .)