Military. a unit of ground forces, consisting of two or more battalions or battle groups, a headquarters unit, and certain supporting units. (Dictionary.com)
A large group of soldiers, or (more generally) any large number of things or people: (Cambridge Dictionary)
A permanent unit of an army typically commanded by a lieutenant colonel and divided into several companies, squadrons, or batteries and often into two battalions. (Oxford Dictionaries)
Archaic: governmental rule. (Merriam – Webster)
A military unit consisting usually of a number of battalions. (Merriam – Webster)
The Regiment of Princes.