Tax shelters stop being fashionable (6)
I believe the answer is:
trendy
'fashionable' is the definition.
('trendy' can be similar in meaning to 'fashionable')
'tax shelters stop' is the wordplay.
'tax' becomes 'try'.
'shelters' means one lot of letters goes inside another.
'stop' becomes 'end' ('end' can be a synonym of 'stop'**).
'try' going around 'end' is 'TRENDY'.
'being' is the link.
(Other definitions for trendy that I've seen before include "all the rage" , "following latest convention" , "Informally in the latest fashion" , "Up to date, fashionable" , "With-it" .)