empire or significant State / realm (also e.g. of plants)

the Holy Roman Empire, the First Reich / the Deutsche Reich; the (Deutsche) Kaiserreich, the Second Reich (1871–1918) / the Deutsche Reich; the Weimar Republic (official name, 1919–1933) / the Deutsche Reich; the Third Reich (1933–1945)

a surname

rich

singular imperative of reichen

-rich, -ful, used to form an adjective from a noun with the sense of 'rich in', 'full of'.

The Third Reich.

Fourth Reich

Used other than figuratively or idiomatically: see das, Reich. / Das Reich (the 2nd SS Division)

singular imperative of ausreichen / first-person singular present of ausreichen