Answer:

loneliest

AnswerCrossword Clue
LONELIESTOne, as numbers go
LONELIEST"One is the ... number that you'll ever do" (Three Dog Night lyric)
LONELIEST"... Star" (Seal song)
LONELIESTDescribing a lighthouse keeper's job.
LONELIESTAdjective for Crusoe.
LONELIESTLeast frequented
LONELIESTLeast attended
LONELIESTThe ... Road in America (Nevada's Highway 50)