Béarnaise saucePronunciation: /ˌbeɪəˈneɪz/Definition of Béarnaise sauce noun [mass noun] a rich sauce thickened with egg yolks and flavoured with tarragon. Origin:Béarnaise, feminine of French béarnais 'of Béarn', a region of SW FranceBéarnaise sauce in other Oxford dictionaries Definition of Béarnaise sauce in the US English dictionary