**6. Conclusions**

The similarity measure and distance measure are widely used in MCMD problems. Considering that the cosine similarity measure proposed by Liao et al. [31] is not a regular similarity measure, a new similarity measure combining the existing cosine similarity measure [31] and the Euclidean distance measure of HFLTSs is proposed, which is constructed based on the linguistic scale function. The proposed similarity measure in this paper considers the distance measure, not only from the point of view of algebra, but also from the point of view of geometry, and it also satisfies the axiom of the similarity measure. As far as we know, the new similarity measure between HFLTSs can express the fuzzy linguistic information more flexibly, which can improve the adaptability of HFLTSs in practice. Furthermore, the TOPSIS method with the corresponding distance measure is developed, and it focuses on the differences for each alternative, which can improve the effectiveness of solving MCDM problems. Finally, a numerical example is given to demonstrate the feasibility and the effectiveness of the proposed method, which is compared to the existing methods. In future research, efforts are continued to find other applications of the proposed similarity measure in the fields of supplier selection, pattern recognition, and so on.

**Author Contributions:** The research is conceptualized and performed by D.L. and Y.L. The paper is written by D.L. and Y.L., and finally checked and revised by X.C. The paper is supervised by X.C. All authors read and approved the final manuscript.

**Funding:** This research was funded by Natural Science Foundation of Hunan (No. 2017JJ2096, 2018JJ3137), the National Natural Science Foundation of China (No. 11501191), the National Social Science Foundation of China (No. 15BTJ028), the outstanding youth project of the Hunan Education Department (No. 1713092) and by Major projects of the National Social Science Foundation of China (17ZDA046).

**Conflicts of Interest:** The authors declare no conflict of interest regarding the publication for the paper.
