Analysed Mother Earth idea (7)
I believe the answer is:
theorem
'idea' is the definition.
(theorem is a kind of idea)
'analysed mother earth' is the wordplay.
'analysed' indicates anagramming the letters.
'earth' becomes 'E'.
'mother'+'e'='mothere'
'mothere' is an anagram of 'THEOREM'.
(Other definitions for theorem that I've seen before include "Geometric proposition" , "speculation" , "A rule in algebra" , "(Maths) proposition" , "Statement to be proved in maths" .)