nosepiece

1. A piece of armor that forms part of a helmet and protects the nose.
2. The part of a pair of eyeglasses that fits across the nose.
3. See noseband.
4. The part of a microscope, often rotatable, to which one or more objective lenses are attached.

The part of a microscope, often rotatable, to which one or more objective lenses are attached.

The noun has 2 meanings:

Meaning #1: armor plate that protects the nose

Meaning #2: the link between two lenses; rests on nose
  Synonym: bridge