passer-by
  過客
  pas·ser·by, Pass·er-by n. One who passes by, especially casually or by chance; one not directly involved in some action; a passer.
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  passer-by
       n : a person who passes by casually or by chance [syn: passerby,
            passer]
       [also: passers-by (pl)]
  passerby
       n : a person who passes by casually or by chance [syn: passer-by,
            passer]