reign

 
Pronunciation: /reɪn/

verb

[no object]
  • hold royal office; rule as monarch: Queen Elizabeth reigns over the UK
  • be the best or most important in a particular area or domain: in America, baseball reigns supreme
  • (of a quality or condition) be the dominant feature of a situation or place: confusion reigned

noun

  • the period of rule of a monarch: the original chapel was built in the reign of Charles I
  • the period during which someone or something is predominant or pre-eminent: she was hoping for a long reign as world champion

Origin:

Middle English: from Old French reignier 'to reign', reigne 'kingdom', from Latin regnum, related to rex, reg- 'king'

The correct idiomatic phrase is a free rein, not a free reign; see rein (usage).