'theoretician' originates from French, specifically the word 'théoréticien', ultimately traceable to Late Latin 'theoreticus' and Greek 'theōretikos', where the root 'theōreō' meant 'to observe' or 'to contemplate'.

'theoretician' changed from the French word 'théoréticien', which came via Late Latin 'theoreticus' from Greek 'theōretikos' (from 'theōreō'), and eventually became the modern English word 'theoretician'.

Initially, it referred to 'one given to contemplation or observation', but over time it evolved into its current meaning of 'a person concerned with theory or theoretical work'.