M*A*S*H actor featured in fashionable Ur (as it was) (8)
I believe the answer is:
chaldaic
'ur as it was' is the definition.
(city of Ur, part of the Chaldean Empire)
'mash actor featured in fashionable' is the wordplay.
'mash actor' becomes 'Alda' (Alan Alda, star of M*A*S*H).
'featured in' indicates putting letters inside.
'fashionable' becomes 'chic' (chic means stylish or fashionable).
'alda' placed within 'chic' is 'CHALDAIC'.
(Other definitions for chaldaic that I've seen before include "from an old region" , "Biblical Aramaic" .)