Collective nouns typically describe groups of things, and they are often associated with specific objects or animals. For example:
* A flock of birds
* A herd of cattle
* A swarm of bees
Perhaps you were thinking of a word that sounds like it starts with "x" but actually has a different spelling, like "a pack" (of wolves) or "a school" (of fish)?
Let me know if you have any other questions!