Energy in motivation daughter gained (7)
I believe the answer is:
derived
'gained' is the definition.
('derive' can be a synonym of 'gain')
'energy in motivation daughter' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mcr).
'in' is an insertion indicator.
'motivation' becomes 'drive' (I've seen this before).
'daughter' becomes 'd' (genealogical abbreviation).
'e' going inside 'drive' is 'derive'.
'derive'+'d'='DERIVED'
(Other definitions for derived that I've seen before include "Formed or developed from something else" , "Traced the source" , "Procured" , "Inferred" , "Obtained/drawn (from)" .)