DOMINUS (from an Indo-European root dam-, cf. Gr., to subdue, and Eng. "tame"), the Latin word for master or owner. As a title of sovereignty the term under the republic at Rome had all the associations of the Greek ; refused during the early principate, it finally became an official title of the Roman emperors under Diocletian. Dominus, the French equivalent being sieur, was the Latin title of the feudal (superior and mesne) lords, and also an ecclesiastical and academical title. The ecclesiastical title was rendered in English "sir," which was a common prefix before the Reformation for parsons, as in "Sir Hugh Evans" in Shakespeare's Merry Wives of Windsor. The academical use was for a bachelor of arts, and so is still used at Cambridge and other universities. The shortened form "dom" is used as a prefix of honour for ecclesiastics of the Roman Church, and especially for members of the Benedictine and other religious orders. The same form is also a title of honour in Portugal, as formerly in Brazil, used by members of the blood royal and others on whom it has been conferred by the sovereign. The Spanish form "don" is also a title, formerly applicable only to the nobility, and now one of courtesy and respect applied to any member of the better classes. The feminine form "donna" is similarly applied to a lady. The English colloquial use of "don" for a fellow or tutor of a college at a university is derived either from an application of the Spanish title to one having authority or position, or from the academical use of dominus. The earliest use of the word in this sense appears, according to the New English Dictionary, in South's Sermons (1660). An English corruption "dan" was in early use as a title of respect, equivalent to "master." The particular literary application to poets is due to Spenser's use of "Dan Chaucer, well of English undefyled" (Faëry Queen, IV. ii. 32).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)