Language somewhat lost on guests (6)
I believe the answer is:
tongue
'language' is the definition.
(tongue is a kind of language)
'somewhat lost on guests' is the wordplay.
'somewhat' indicates a hidden word.
'TONGUE' is hidden in the letters of 'lost on guests'.
(Other definitions for tongue that I've seen before include "cold meat?" , "Language; part of shoe" , "Part of shoe or mouth" , "Mouth organ; language" , "'Red lorry, yellow lorry', for example" .)