My fascination with the way the meaning of words evolves will never falter. In the case of the French merci, it is interesting that the first sense of the Latin mercedem was “reward, grace, favor“. The meaning is then somehow projected onto the one who receives a favor, hence the sense of gratitude, while Italian and Spanish remained closer gratias in Latin. In English, thank, comes from the Indo-European root think, “think”, which then meant “good thought,” and finally “gratitude”. It seems that despite the variety of the roots, the importance of the words seems to be agreed upon in most languages.