The word seems originally to have indicated an officer connected with a tribe (tribus), or who represented a tribe for certain purposes; and this is indeed the character of the officers who were designated by it in the earliest times of Rome, and may be traced also in the later officers of this name.

Definition of the Roman Tribune (Tribunus)
The Definition of a Roman Tribune is as follows: An officer or magistrate chosen by the people, to protect them from the oppression of the patricians, or nobles, and to defend their liberties against any attempts that might be made upon them by the senate and consuls. The tribunes were at first one, but their number was increased ultimately to ten. There were also military tribunes, officers of the army, of whom there were from four to six in each legion. Other officers were also called tribunes; as, tribunes of the treasury, etc.

Roman Tribune Ranks
The following details Roman Tribune Ranks:

• Tribune (Latin:Tribunus) One of six assistants to a legion commander, the Primus Pilus. Usually a young senator learning the basics for his career
• Tribunus Cohortis: Commander of a Cohort military unit
• Tribunus Cohortis Urbanae: Urban cohort commander.

History of the Roman Tribune
Originally there was one Roman Tribune in each legion from the three tribes called the the Ramnes, Luceres, and Tities. In the time of Polybius the number in each legion was six. The authority of the Roman Tribune extended equally over the whole legion; but to prevent confusion, it was the custom for them to divide into three sections of two, and each pair undertook the routine duties for two months out of six. The Tribunes nominated the centurions, and assigned each to the company to which he belonged. These tribunes at first were chosen the commanders-in-chief, by the kings and consuls; but during the days of the republic, when the patrician power was pre-eminent, they were elected by the people, that is, the Roman citizens. Later they were named, half by the Senate and half by the consuls. No one was eligible to this great office who had not served ten years in the infantry or five in the cavalry.

Clothing of the Military Roman Tribune
The Roman tribunes were distinguished by their dress from the common soldier. Many Tribunes were aristocrats drawn from the upper social class. They wore the same basic equipment, though it is likely that the higher ranks had more heavily decorated armor. Their Cuirass, or breastplate was defensive armor for the torso, worn over a cloth, leather, or padded vest. These breastplates which were often molded to form "anatomical" cuirasses. The lower edge of the cuirass was curved and had one or more rows of round or long tongue-shaped lappets (pteryges) which formed a skirt. There may also have been differences in the color of certain garments, for instance the cloak of a Roman Tribune was usually red. This large rectangular cloak was called the paludamentum and was typically pinned or fixed to the right shoulder, so as not to impede the movement of the right arm, with a clasp, called a fibula. The paludamentum was often draped or wrapped around the left arm. Putting on the paludamentum was a ceremonial act on setting out for war.