'Nebular hypothesis' definitions:

Definition of 'nebular hypothesis'

noun

(cosmology) the theory that the solar system evolved from a hot gaseous nebula

From: GCIDE

Hypothesis \Hy*poth"e*sis\, n.; pl. Hypotheses. [NL., fr. Gr. ? foundation, supposition, fr. ? to place under, ? under + ? to put. See Hypo-, Thesis.]
1. A supposition; a proposition or principle which is supposed or taken for granted, in order to draw a conclusion or inference for proof of the point in question; something not proved, but assumed for the purpose of argument, or to account for a fact or an occurrence; as, the hypothesis that head winds detain an overdue steamer. [1913 Webster]
An hypothesis being a mere supposition, there are no other limits to hypotheses than those of the human imagination. --J. S. Mill. [1913 Webster]
2. (Natural Science) A tentative theory or supposition provisionally adopted to explain certain facts, and to guide in the investigation of others; hence, frequently called a working hypothesis.
Syn: Supposition; assumption. See Theory. [1913 Webster]
Nebular hypothesis. See under Nebular. Hypothetic

From: GCIDE

Nebular \Neb"u*lar\, a. Of or pertaining to nebulae; of the nature of, or resembling, a nebula. [1913 Webster]
Nebular hypothesis, an hypothesis to explain the process of formation of the stars and planets, presented in various forms by Kant, Herschel, Laplace, and others. As formed by Laplace, it supposed the matter of the solar system to have existed originally in the form of a vast, diffused, revolving nebula, which, gradually cooling and contracting, threw off, in obedience to mechanical and physical laws, succesive rings of matter, from which subsequently, by the same laws, were produced the several planets, satellites, and other bodies of the system. The phrase may indicate any hypothesis according to which the stars or the bodies of the solar system have been evolved from a widely diffused nebulous form of matter. [1913 Webster]