Miserable husband initially under one choosing austerity (5)
I believe the answer is:
sadhu
'one choosing austerity' is the definition.
(I've seen this before)
'miserable husband initially under' is the wordplay.
'miserable' becomes 'sad' (similar in meaning).
'husband' becomes 'h'.
'initially' suggests taking the first letters.
The first letter of 'under' is 'u'.
'sad'+'h'+'u'='SADHU'
(Other definitions for sadhu that I've seen before include "one choosing austerity" , "Indian wandering holy man" , "Ascetic" , "Hindu wandering holy man" , "Indian holy man or sage" .)