Cranial nerve and First cranial nerve

Cranial nerve noun - Any of the 12 paired nerves that originate in the brain stem.

First cranial nerve and cranial nerve are semantically related. In some cases you can replace phrase "First cranial nerve" with "Cranial nerve", this phrases are similar.

First cranial nerve noun - A collective term for numerous olfactory filaments in the nasal mucosa.

Cranial nerve and first cranial nerve are semantically related. You can use "Cranial nerve" instead a noun phrase "First cranial nerve".