nebulous

Nebulous is an English adjective with two primary senses. In general usage, it means vague, indistinct, or lacking a clearly defined form or limit. Something described as nebulous may be unclear, ill-defined, or open to interpretation, such as a plan with nebulous objectives or a policy with nebulous guidelines. The sense emphasizes a lack of precise boundaries rather than a physical blur.

In astronomy, nebulous describes something relating to a nebula or to a diffuse, cloud-like appearance in the sky. A nebula is a vast cloud of gas and dust in space; an object described as nebulous can have a fuzzy edge or a hazy, cloudlike appearance when viewed through telescopes or recorded in images. The term can apply to regions of space that are not sharply defined, as well as to objects that resemble a nebula even if not literally classified as one.

Etymology: nebulous comes from the Latin nebulosus 'cloudy, foggy,' from nebula 'cloud, mist,' ultimately from a root meaning cloud. The word entered English in the early modern period, used both in figurative and astronomical contexts.

Usage: Nebulous is common in academic, journalistic, and literary writing when describing unclear ideas, definitions, or plans. In astronomy, more precise terms such as nebula, nebular, or specific class names (emission nebula, planetary nebula) are often preferred, but nebulous remains acceptable to describe diffuse or ill-defined features.