Glib complaint about ten (6)
I believe the answer is:
fluent
'glib' is the definition.
(thesaurus)
'complaint about ten' is the wordplay.
'complaint' becomes 'flu' (flu is a kind of disease).
'about' indicates anagramming the letters.
'ten' with letters rearranged gives 'ent'.
'flu'+'ent'='FLUENT'
(Other definitions for fluent that I've seen before include "(Highly proficient) in a foreign language" , "Spoken with facility" , "Easily flowing" , "well able to interpret" , "Using (language) easily" .)