Definition of main guard in US English:

main guard

noun

  • Military. A body of troops constituting the chief guard, especially a body of cavalry posted on the wings of a camp towards the enemy; a guard in a fortress taking custody of disturbers of the peace, etc.

Origin

Mid 17th century; earliest use found in Henry Hexham (fl. 1601–1650), soldier and author. From main + guard.

Pronunciation

main guard

/ˈmeɪn ˌɡɑːd/