Ordinal number (linguistics) in the context of "Greek numerals"

A regnal year is a year of the reign of a sovereign, from the Latin regnum meaning kingdom, rule. Regnal years considered the date as an ordinal, not a cardinal number. For example, a monarch could have a first year of rule, a second year of rule, a third year of rule, and so on, but not a zeroth year of rule.

Applying this ancient epoch system to modern calculations of time, which include zero, is what led to the debate over when the third millennium began. Regnal years are "finite era names", contrary to "infinite era names" such as Christian era, Jimmu era, Juche era, and so on.

The ten Heavenly Stems (or Celestial Stems) are a system of ordinals indigenous to China and used throughout East Asia, first attested c. 1250 BCE during the Shang dynasty as the names of the ten days of the week. They were also used in Shang-era rituals in the names of dead family members, who were offered sacrifices on the corresponding day of the Shang week. Stems are no longer used as names for the days of the week, but have acquired many other uses. Most prominently, they have been used in conjunction with the associated set of twelve Earthly Branches in the compound sexagenary cycle, an important feature of historical Chinese calendars.

Regnal numbers are ordinal numbers—often written as Roman numerals—used to distinguish among persons with the same regnal name who held the same office, notably kings, queens regnant, popes, and rarely princes and princesses.

It is common to start counting either since the beginning of the monarchy, or since the beginning of a particular line of state succession. For example, Boris III of Bulgaria and his son Simeon II were given their regnal numbers because the medieval rulers of the First and Second Bulgarian Empire were counted as well, although the recent dynasty dates only back to 1878 and is only distantly related to the monarchs of previous Bulgarian states. On the other hand, the kings of England and kings of Great Britain and the United Kingdom are counted starting with the Norman Conquest. That is why the son of Henry III of England is called Edward I, even though there were three English monarchs named Edward before the Conquest (they were distinguished by epithets instead).

101 (one hundred [and] one) is the natural number following 100 and preceding 102.

It is variously pronounced "one hundred and one" / "a hundred and one", "one hundred one" / "a hundred one", and "one oh one". As an ordinal number, 101st (one hundred [and] first), rather than 101th, is the correct form.