a small cluster of indistinct stars having the appearance of a single hazy star; (also) a star with a large gaseous atmosphere giving it a hazy…

Astronomy. Originally: an indistinct cloud-like, luminous object seen in the night sky, such as a cluster of distant stars, a galaxy, or a cloud of…

A nebulous star, a nebula. Obsolete. rare.

A nebula (nebula, n. 2). Chiefly figurative.

an assemblage of many stars in (real or apparent) proximity; a large star cluster.