An Etymological Dictionary of the German Language/Annotated/Trost
Trost, masculine, ‘comfort, consolation,’ from Middle High German and Old High German trôst, masculine, ‘comfort, help, protection, assurance, confidence’; corresponding to Old Icelandic traust, masculine, ‘assurance,’ Gothic traust (genitive traustis for -eis), ‘treaty, alliance.’ The word is a derivative of the Teutonic root traus, a variant of the root trū̆ appearing in trauen. Compare Old Icelandic traustr, adjective, ‘certain, strong, firm,’ literally ‘that in which one has confidence.’ —