Outside hotel, met up with English subject (5)
I believe the answer is:
'subject' is the definition.
(theme can mean a topic or subject)
'outside hotel met up with english' is the wordplay.
'outside' indicates putting letters inside.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'up with' indicates an anagram (letters get chucked up).
'english' becomes 'e' (abbreviation).
'met' mixed up with 'e' can make 'teme'.
'h' inserted inside 'teme' is 'THEME'.
(Other definitions for theme that I've seen before include "Topic for discussion" , "Subject matter, motif" , "Motif - 4 across" , "(Writer's) topic" , "notedly subject to variation" .)