Endlessly suave, yet uncertain (4)
I believe the answer is:
moot
'uncertain' is the definition.
(thesaurus)
'endlessly suave' is the wordplay.
'endlessly' indicates the central letters (the ends of the words are removed).
'suave' becomes 'smooth' (synonyms).
The middle letters of 'smooth' are 'MOOT'.
'yet' acts as a link.
(Other definitions for moot that I've seen before include "raise for discussion" , "Anglo-Saxon assembly; subject to debate" , "Such a point is arguable" , "Questionable, debatable" , "Propose for discussion" .)