Free Double Hierarchy Hesitant Fuzzy Linguistic Term Sets: An application on ranking alternatives in GDM.

•Some issues of the Double Hierarchy Hesitant Fuzzy Linguistic Term Sets are fixed.•A new mathematical structure to deal with linguistic assessments is defined.•This structure enables the experts to be more precise by choosing their own scale.•A new approach of the TOPSIS methodology based on this structure is presented.•A case study based on tourism management in Barcelona is provided.