Note: The form 'trouser' is used as a modifier.
1.
Trousers are a piece of clothing that you wear over your body from the waist downwards, and that cover each leg separately. (mainly BRIT; in AM, usually use pants )
He was smartly dressed in a shirt, dark ~ and boots...
Alexander rolled up his trouser legs.
N-PLURAL: also a pair of N
2.
to wear the ~: see wear