tailer

noun

1. One who follows or tails surreptitiously, as an investigator.

   “I had to concentrate on staying out of sight, yet close enough not to be stranded on the wrong side of a stoplight. I was working so hard at it that I didn't notice that the tailer had become the tailee.”

   “When the car entered the traffic circle I followed after it, the tailed now tailing the tailer. The car's occupants, sure now that they'd been spotted, sped off ahead of me along Dodgers Hole Road.”

   “he became aware that he was being tailed. ... turned the action around and tailed the tailer, and then realized that the tailer had not been tailing him”

2. A worker on a yacht, responsible for furling and setting the sails.

   “The next step was the invention of the self-tailing device, whereby the need for a tailer, holding the sheet or halyard while another person operated the winch, was eliminated.”

3. A large noose with a long handle intended to secure a fish's tail.
4. A fish bottom-feeding in shallow water with its tail out of the water.