Sound, fancy belt encircling Ena (7)
I believe the answer is:
tenable
'sound' is the definition.
(both can mean solid or viable)
'fancy belt encircling ena' is the wordplay.
'fancy' indicates anagramming the letters.
'encircling' is an insertion indicator.
'belt' with letters rearranged gives 'tble'.
'tble' going around 'ena' is 'TENABLE'.
(Other definitions for tenable that I've seen before include "Of argument, rational and defensible" , "Well-founded" , "Possible to be defended" , "possible to maintain" , "fairly arguable" .)