CIA men relaxed in picture-house (6)
I believe the answer is:
cinema
'picture-house' is the definition.
(I've seen this before)
'cia men relaxed in' is the wordplay.
'relaxed' is an anagram indicator.
'in' means one lot of letters goes inside another.
'men' is an anagram of 'nem'.
'cia' placed around 'nem' is 'CINEMA'.
(Other definitions for cinema that I've seen before include "Films, collectively" , "Movie-house" , "(Building for) the movies" , "(Building showing) films" , "Silver screen" .)