outer
adjective
ˈaʊtə(r) 
ˈaʊtər 
1 on the outside of somethingSynonym
externalthe outer layers of the skin2 furthest from the inside or centre of somethingI walked along the outer edge of the track.the outer suburbs of the cityOuter London/Mongolia (figurative) to explore the outer (= most extreme) limits of human experienceOpposite
inner