The word 'titre' entered English in the 19th century with a specific scientific meaning, diverging from its more general French source. Its journey begins with the Latin 'titulus', denoting an inscription or placard, which evolved in Old French to 'title', referring to an appellation or heading. In French, 'titre' developed a specialized financial and chemical sense relating to the fineness of gold or the concentration of a solution. English adopted this precise technical sense directly from French, applying it primarily in analytical chemistry and immunology to denote a measured concentration or strength. Thus, a word rooted in the concept of a public label transformed into a term for a precise quantitative value determined through laboratory procedure.

The word 'titre' is a direct borrowing from French, where it originally meant "title". It is a simplex word in English, derived from the Old French 'title', which came from Latin 'titulus' meaning "label, inscription, title of honor".