Humble-sounding manner (4)
I believe the answer is:
mean
'humble' is the definition.
(thesaurus)
'sounding manner' is the wordplay.
'sounding' indicates a 'sounds like' (homophone) clue.
'manner' becomes 'mien' (mien can mean a manner or attitude).
'mien' is a homophone of 'MEAN'.
(Other definitions for mean that I've seen before include "Unkind; average" , "Intend; unkind" , "Close" , "show" , "Relating to flowers" .)