Ruling; governing; regnant.

One who rules or reigns; a governor; a ruler.

A person who reigned on behalf of a monarch who for some reason could not. George III went permanently insane in 1810.* His son, the Prince of Wales, later George IV thereupon became the prince regent. *A condition which we now know was due to porphyria.

someone who rules during the absence or incapacity or minority of the country's monarch

acting or functioning as a regent or ruler; "prince-regent"

an individual who rules in the name of another individual, normally one who is to young to actually rule

a person or group selected to govern in place of a monarch or other ruler who is absent, disabled or too young

a person who rules during the absence, incapacity or minority of the country's monarch

a person who rules for a child until the child is old enough to take over

Regent, from the Latin, a person selected to administer a state because the ruler is a minor or is not present or debilitated. Thus, the common use is for an acting deputy governor. The Oxford English Dictionary defines the term as "A person appointed to administer a State because the monarch is a minor, is absent or is incapacitated."