protector

Concise Oxford English Dictionary © 2008 Oxford University Press:
protector/prəˈtektə(r)/

▶noun

• 1 a person or thing that protects.

• 2 (Protector) historical a regent in charge of a kingdom during the minority, absence, or incapacity of the sovereign.

  ■ (also Lord Protector of the Commonwealth) the title of Oliver Cromwell and his son Richard as heads of state in England 1653–9.

– derivatives
protectoral adjective,
protectorship noun,
protectress noun.