Kind of power or family (7)
I believe the answer is:
nuclear
This clue is a double definition.
'kind of power' is the first definition.
'family' is the second definition.
(nuclear family is a kind of family)
(Other definitions for nuclear that I've seen before include "kind of war" , "winter, sort of" , "In sociology, of a family of parents and offspring only" , "power source" , "type of power supply" .)