ADEPT (if used as a substantive pronounced adept, if as an adjective adept; from Lat. adeptus, one who has attained), completely and fully acquainted with one's subject, an expert. The word implies more than acquired proficiency, a natural inborn aptitude. In olden times an adept was one who was versed in magic, an alchemist, one who had attained the great secrets of the unknown.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)