outer (adj.)youdaoicibaDictYouDict[outer 词源字典]
late 14c., comparative of out (on analogy of inner), replacing by 18c. forms descended from Old English uttera (comp. of Old English ut "out") which developed into utter and was no longer felt as connected with out. Outer space first attested 1901 in writings of H.G. Wells.[outer etymology, outer origin, 英语词源]