Peer (Lat. par, equal; Fr. pair), a term originally applied, in the feudal law, to all the vassals of the same lord, because, whatever might be their relative condition, they were all equally his vassals, and bound to render their feudal service in his courts or in war. It is now applied sometimes to those who are impanelled in an inquest for trial of any person; for they are not only peers with each other, as having equal power and an equal duty, but by the common law of England every man is to be tried "by his peers." In the United States this principle has no practical application, as all are equal in law where no one has any legal rank. In England the word is most commonly used to designate a lord of parliament, all of whom are called the " king's peers," not because they are in any sense equal with the king, but because they constitute his highest court, and because, whatever may be the degree of their nobility, all, as nobles, are equal in the discharge of their official duty, as in their votes in parliament, or upon the trial of any person impeached by the commons; and all share alike in all the privileges of the peerage. The different degrees of English nobility are, in the order of precedence, duke, marquis, earl, viscount, and baron.

The eldest son of the first three is usually called by his father's second title, and their other sons by the term lord prefixed to their family names. These titles are called titles of courtesy, their bearers having no legal right to them. The sons of a viscount are called honorable. In the British empire there are five classes of peerage: of England, of Great Britain, of the United Kingdom, of Scotland, and of Ireland. Members of the first three classes, called peers of the realm, hold seats in the house of lords by hereditary right; those of the last two only by election as representatives of their order. (See Parliament.) A peeress is a woman who is noble by descent, by creation, or by marriage. A peeress by descent or by creation retains her title and nobility in law, although she marries a commoner; but a peeress by marriage loses her nobility by her marriage with a commoner, though she commonly retains her title in society as a title of courtesy. It is one of the privileges of the peerage of the realm not to be liable to arrest for debt.

This rule applies equally to peeresses, who are peers of the realm, and can only be tried by their peers, although they cannot sit in parliament or on trials. - In France, as a kingdom and an empire, the word pair remained in use through all the governments from feudal times; but the functions and privileges of the peerage varied very much at different'times, the term being destitute of the definite meaning which it has attained in England. Louis XVIII. in 1814 established a house of lords (pairs), or more accurately a peerage, in some degree resembling the English system; but Villele, the minister of Charles X., created at one time 76 new peers, when he wanted them for a political purpose.