The word 'tansy' entered English in the medieval period from the Old French 'tanesie'. This French term derived from the Medieval Latin 'tanacetum', which was an alteration of the Late Latin 'athanasia'. This Latin word was borrowed from the Greek 'athanasia', literally meaning 'immortality' (from 'a-' meaning 'not' + 'thanatos' meaning 'death'). The semantic link is thought to be either from the plant's long-lasting flowers or, more likely, from its historical use in medicinal preparations intended to prolong life or as a preservative. Over centuries, the word's form contracted and simplified from 'athanasia' to 'tanacetum' and finally to the monosyllabic English 'tansy', while its meaning narrowed specifically to denote the aromatic, yellow-flowered herb.

The word 'tansy' is a simplex word borrowed from Old French. Its ultimate origin is the Medieval Latin 'tanacetum' or 'athanasia', from Greek 'athanasia', meaning 'immortality'. The functional role of the word as a whole is to name a specific plant.