Horizon (7)
'horizon' is the definition.
(I know that horizon can be written as skyline)
This is the entire clue.
(Other definitions for skyline that I've seen before include "Horizon; like NY's (anag.)" , "Visible horizon" , "Outline of hills or buildings against firmament" , "Silhouette or outline of buildings" , "City horizon" .)
(Other definitions for lost that I've seen before include "Not knowing one's whereabouts" , "Unable to find one's way" , "See 10" , "Mislaid or astray" , "Not having known where one is" .)