One of a board or body of municipal officers next in order to the mayor and having a legislative function. They may, in some cases, individually exercise some magisterial and administrative functions.
Derived from O.E. ealdorman and surviving in urban usage to describe the holder of a senior civic office. Two main usages are (I) the chief officer of a guild: occurs in the earlier Middle Ages and later in surviving merchant guilds; (II) the member of a town council, particularly an upper council: increasingly common in the later Middle Ages, probably under London influence. (Reynolds, Susan. An Introduction to the History of English Medieval Towns, 197)