Proposition earth mother prepared to embrace (7)
I believe the answer is:
theorem
'proposition' is the definition.
(theorem is a kind of proposition)
'earth mother prepared to embrace' is the wordplay.
'earth' becomes 'E'.
'prepared' indicates an anagram.
'to embrace' is an insertion indicator.
'mother' is an anagram of 'theorm'.
'e' going into 'theorm' is 'THEOREM'.
(Other definitions for theorem that I've seen before include "deduction" , "Mathematical statement to be proved" , "speculation" , "Algebraic rule" , "Geometric proposition" .)