trooper

Concise Oxford English Dictionary © 2008 Oxford University Press:
trooper/ˈtruːpə(r)/

▶noun

• 1 a private soldier in a cavalry or armoured unit.

  ■ a cavalry horse.

  ■ chiefly Brit. a troopship.

• 2 chiefly US a mounted police officer.

  ■ US a state police officer.

– phrases
swear like a trooper swear a great deal.