European resort hotel covering up immorality (7)
I believe the answer is:
spanish
'european' is the definition.
(Spain is part of Europe)
'resort hotel covering up immorality' is the wordplay.
'resort' becomes 'spa' (spa is a kind of resort).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'covering' is an insertion indicator.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'immorality' becomes 'sin' (sin is a kind of immorality).
'sin' written backwards gives 'nis'.
'spa'+'h'='spah'
'spah' placed around 'nis' is 'SPANISH'.
(Other definitions for spanish that I've seen before include "European language used in other countries" , "His pans are from Barcelona, say" , "Language of much of Central America" , "Language of much of the New World" , "Pin sash up for the language" .)