Vigorously active husband permitted one to enter Air Training Corps (8)
I believe the answer is:
athletic
'vigorously active' is the definition.
(I've seen this before)
'husband permitted one to enter air training corps' is the wordplay.
'husband' becomes 'h' (abbreviation).
'permitted' becomes 'let' (to let something happen is to permit it).
'one' becomes 'i' (Roman numeral).
'to enter' is an insertion indicator.
'air training corps' becomes 'ATC' (abbreviation).
'h'+'let'+'i'='hleti'
'hleti' going into 'atc' is 'ATHLETIC'.
(Other definitions for athletic that I've seen before include "Sporty, able-bodied" , "Strong and vigorous" , "Active and fit for sport etc" , "Lithe act (anag)" , "Strong and sporty" .)