Ran miles to embrace that chap? That’s the idea (7)
I believe the answer is:
theorem
'the idea' is the definition.
(theorem is a kind of idea)
'ran miles to embrace that chap?' is the wordplay.
'ran' becomes 'tore' (I've seen this before).
'miles' becomes 'm' (common abbreviation).
'to embrace' is an insertion indicator.
'that chap?' becomes 'he'.
'tore'+'m'='torem'
'torem' placed around 'he' is 'THEOREM'.
'that's' is the link.
(Other definitions for theorem that I've seen before include "Formula to be proved" , "Statement to be proved in maths" , "Geometric proposition" , "speculation" , "Mathematical axiom" .)