cluster fly

noun

: a large dark-brown fly (Pollenia rudis) related to the bluebottles and often gathering in large clusters in attics and other sheltered places during cool autumn weather

The Ultimate Dictionary Awaits

Expand your vocabulary and dive deeper into language with Merriam-Webster Unabridged.

1. Expanded definitions
2. Detailed etymologies
3. Advanced search tools
4. All ad-free

Discover what makes Merriam-Webster Unabridged the essential choice for true word lovers.

Start Your Free Trial Now