Full Idea
A cosmos is a circumscribed portion of the heavens containing stars and an earth; it is separated from the unlimited, with a boundary which is rare or dense; it is revolving or stationary; it is round or triangular, or some shape. All these are possible.
Gist of Idea
A cosmos is a collection of stars and an earth, with some sort of boundary, movement and shape
Source
Epicurus (Letter to Pythocles [c.292 BCE], 88)
Book Reference
Epicurus: 'The Epicurus Reader', ed/tr. Inwood,B. /Gerson,L. [Hackett 1994], p.20
A Reaction
Notice that there seem to exist the 'heavens' which extend beyond the cosmos. See Idea 14036, saying that there are many other cosmoi in the heavens.
Related Idea
Idea 14036 There are endless cosmoi, some like and some unlike this one [Epicurus]