Fellow joins the Spanish church (6)
I believe the answer is:
chapel
'church' is the definition.
(I've seen this before)
'fellow joins the spanish' is the wordplay.
'fellow' becomes 'chap' (synonyms).
'joins' is a charade indicator (letters next to each other).
'the spanish' becomes 'el' ('the' in Spanish).
'chap'+'el'='CHAPEL'
(Other definitions for chapel that I've seen before include "Perhaps part of cathedral" , "Part of a large church" , "house of prayer" , "Small building for worship" , "service" .)