Academic - academician

The noun academician is not, in the UK, a more impressive or formal way of saying academic - although OED does record this as meaning 1.: "= academic n. 3. [...a member of a university or college's teaching or research staff...] Now chiefly U.S." (AWE's emphasis).

• So the most usual meaning of academic, as a noun, in UK is 'a person professionally engaged in Higher Education', 'a professor or lecturer (or one aspiring to that status)'. For more meanings, see Academic.
• An academician, in British English, is a member of an officially constituted Academy, such as the Royal Academy, the pinnacle of the career of a traditional artist; the British Academy, to be elected to which is a great honour for scholars in the humanities; and the Académie Française, whose 40 members, entrusted with the care of the French language, are also known by their (slightly) less formal nickname of Les Immortelles ('the Immortals').

These two words used to be more or less interchangeable. Modern writers however are advised to keep them apart.

In the early days of the Academies, in the 17th century, and for some time afterwards, members were also called academists; rather later, the word academical was also used. Both these words should be considered obsolete in this sense: don't use them.