earl n.

title of nobility in some continental nations, corresponding to English earl, c. 1300, from Anglo-French counte "count, earl" (Old French conte), from Latin comitem (nominative comes) "companion, attendant," the Roman term for a provincial governor, from com "with" (see com-) + stem of ire "to go" (from PIE root *ei- "to go"). The term was used in Anglo-French to render Old English eorl, but the word was never truly naturalized and mainly was used with reference to foreign titles.

In ancient Rome and the Roman empire, [a comes was] a companion of or attendant upon a great person; hence, the title of an adjutant to a proconsul or the like, afterward specifically of the immediate personal counselors of the emperor, and finally of many high officers, the most important of whom were the prototypes of the medieval counts. [Century Dictionary]

Old English aldormonn (Mercian), ealdormann (West Saxon) "Anglo-Saxon ruler, prince, chief; chief officer of a shire," from aldor, ealder "patriarch" (comparative of ald "old;" see old) + monn, mann "man" (from PIE root *man- (1) "man").

Presumably originally of elders of the clan or tribe, but already in Old English used for king's viceroys, regardless of age. In later Old English a more specific title, "chief magistrate of a county," having both civic and military duties. The word yielded under Canute to eorl (see earl), and after the Norman Conquest to count (n.). Having lost its specific sense, alderman was then applied to any head man; meaning "headman of a guild" (early 12c.) passed to "magistrate of a city" (c. 1200) as the guilds became identified with municipal government. Related: Aldermancy; aldermanic.