Collective nouns for Gnats include a cloud, a horde, a swarm, and a rabble. The collective nouns a cloud, a horde, and a swarm refer to the large numbers of Gnats that can be seen in the air at any given time. The term ‘cloud’ is derived from the fact that large numbers of Gnats can form a visible cloud in the sky. The term ‘horde’ means a large group of people or animals. The term ‘swarm’ means to move in a large group. All of these collective nouns accurately describe the large numbers of Gnats that can be seen in the air.