What is a group of Definitions called?

A group of definitions is commonly called a Dictionary. Other collective nouns you may see include Glossary and Compilation.

Collective nouns are a specific type of noun that refers to a group of individuals or things as a single entity with a singular form. These nouns not only highlight the group's unity but also enable concise and efficient communication by consolidating multiple individuals or objects into a single word. Collective nouns can cover a wide range of subjects, including people, animals, and objects. Examples commonly encountered in the English language include terms such as "herd" for a group of cattle or "team" for a group of individuals working together towards a common goal. More specific instances can be found in expressions like a "choir" of singers, a "fleet" of ships, or an "orchestra" of musicians. These nouns often carry a sense of collective identity or shared characteristics within the group. They evoke a visual image of various individuals functioning cohesively, exhibiting coordinated behavior, or possessing common traits. Phrases like "a flock of birds," "a pack of wolves," or "a school of fish" emphasize the distinctive behavior or nature of the group as a whole. While collective nouns take singular forms grammatically, they can represent anywhere from just a few members up to an abundant multitude. This flexibility enables versatile usage, accommodating both larger entities like a "crowd" or "horde" and smaller ones like a "family" or "committee." Collectively describing a group rather than distinguishing individual members allows for clear, concise, and vivid communication. Collective nouns not only provide a practical way to refer to groups but also have the added benefit of enhancing language usage and aesthetics. They enrich speech and writing by conveying a sense of unity, presenting vivid imagery, and preempting the need for lengthy descriptions. Whether it's describing an assemblage of people, a cluster of objects, or an aggregation of creatures, collective nouns offer an efficient and effective means of communication.