sin ‧ cer ‧ i ‧ ty /sɪnˈserəti, sɪnˈserɪti/ BrE AmE noun [uncountable]
when someone is sincere and really means what they are saying OPP insincerity :
I don’t doubt her sincerity, but I think she’s got her facts wrong.
May I say in all sincerity that we could not have achieved this much without your help and support.