Different in motel, seriously (4)
I believe the answer is:
else
'different' is the definition.
(synonyms)
'in motel seriously' is the wordplay.
'in' indicates a hidden word.
'ELSE' can be found hidden inside 'motel seriously'.
(Other definitions for else that I've seen before include "Other than (what is under consideration)" , "Eels (anag)" , "Besides, otherwise" , "Otherwise; different from" , "Besides; instead" .)