A legion is a horde or a large number of people or things. It was originally a term for a military unit.

In Roman times, a legion was a large unit of men in the army, and the word is still used in many militaries. However, it also means a whole bunch of people doing anything. If someone has many fans, you can say legion of fans or legions of fans, but either way, that's a lot of fans. There are legions of stars in the sky. When you see legion, you can be sure there's an awful lot of something.

Definitions of legion

n a large military unit

“the French Foreign Legion
foreign legion
a military unit composed of foreign volunteers who serve the state
French Foreign Legion
a former foreign legion in the French army that was used for military duties outside of France
Type of:
force, military force, military group, military unit
a unit that is part of some military service

n association of ex-servicemen

“the American Legion
Type of:
a formal organization of people or groups of people

n archaic terms for army

Roman Legion
a division of from 3000 to 6000 men (including cavalry) in the Roman army
(plural) hosts or armies; used in the book of Romans in the New Testament
Type of:
army, ground forces, regular army
a permanent organization of the military land forces of a nation or state

n a vast multitude

horde, host
Type of:
concourse, multitude, throng
a large gathering of people

adj amounting to a large indefinite number

“Palomar's fans are legion
a quantifier that can be used with count nouns and is often preceded by `as' or `too' or `so' or `that'; amounting to a large but indefinite number

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