open cluster

noun

: a cluster of stars in which all the individual members may be discerned with an optical aid and which is much less compact and has fewer members than a globular cluster

often : a galactic cluster

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