"that is farther out, that is exterior or external; of or pertaining to the outside; further removed," late 14c., comparative of out (on analogy of inner), replacing by 18c. forms descended from Old English uttera (comparative of Old English ut "out") which developed into utter (adj.) and was no longer felt as connected with out. Outer space "region beyond the earth's atmosphere" is first attested in H.G. Wells' "The First Men in the Moon" (1901).