The Collaborative International Dictionary of English v.0.48:

Marline \Mar"line\, n. [LG. marlien, marling, or D. marling,
   marlijn, fr. D. marren to tie, prob. akin to E. moor, v., and
   lijn line: cf.F. merlin. See Moor, v., Line.] (Naut.)
   A small line composed of two strands a little twisted, used
   for winding around ropes and cables, to prevent their being
   weakened by fretting.
   [1913 Webster]

   Marline spike, Marling spike (Naut.), an iron tool
      tapering to a point, used to separate the strands of a
      rope in splicing and in marling. It has an eye in the
      thick end to which a lanyard is attached. See Fid.
      [Written also marlin spike]

   Marline-spike bird. [The name alludes to the long middle
      tail feathers.] (Zool.)
   (a) A tropic bird.
   (b) A jager, or skua gull.
       [1913 Webster]