A nomenclator is derived from the Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 nomen- name + calare - to call. In classical

Classical antiquity

Classical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world...

 times it referred to a slave whose duty was to recall the names of persons his master met during a political campaign. Later this became names of people in any social context and included other socially important information.

However, it has taken on several other meanings and also refers to a book containing collections or lists of words. It also denotes a person, generally a public official

Official

An official is someone who holds an office in an organization or government and participates in the exercise of authority .A government official or functionary is an official who is involved in public...

, who announces the names of guests at a party or other social gathering or ceremony

Ceremony

A ceremony is an event of ritual significance, performed on a special occasion. The word may be of Etruscan origin.-Ceremonial occasions:A ceremony may mark a rite of passage in a human life, marking the significance of, for example:* birth...

.

In more general terms still, it is a person who provides or creates the names for things. and this can apply to the application of names in a scientific or any other context but especially in relation to specialist terminologies, glossaries etc.