Theater, the last word in comfort originally, heading west (6)
I believe the answer is:
cinema
'theater' is the definition.
(cinema is a kind of theater)
'the last word in comfort originally heading west' is the wordplay.
'the last word' becomes 'amen' (I've seen this before).
'originally' indicates taking the first letters.
'heading west' says the letters should be written in reverse.
The initial letters of 'in comfort' is 'ic'.
'amen'+'ic'='amenic'
'amenic' in reverse letter order is 'CINEMA'.
(Other definitions for cinema that I've seen before include "(Building showing) films" , "Silver screen" , "Filmdom" , "Movie house" , "Picture house" .)