Wait on guests, taking in language (6)
I believe the answer is:
tongue
'language' is the definition.
(tongue is a kind of language)
'wait on guests taking in' is the wordplay.
'in' indicates a hidden word.
'TONGUE' can be found hidden inside 'wait on guests taking'.
(Other definitions for tongue that I've seen before include "Style of speaking; lick" , "Projecting strip" , "They are hard to say" , "For example, Danish" , "dialect" .)