Option 1 -> "Tiny" refers to something very small in size, not related to clarity or definition.
Option 2 -> "Vague" means unclear, indefinite, or lacking clear form, which matches the meaning of nebulous.
Option 3 -> "Insignificant" means unimportant or trivial, which doesn't capture the essence of nebulous.
Option 4 -> "Dead" means lifeless or no longer living, completely unrelated to the concept of nebulous.
Hence, Option 2: Vague -> "Nebulous" literally means cloudy or hazy (from the word "nebula"), and figuratively describes something that is unclear, ill-defined, or lacking definite form - exactly what "vague" means -> correct