The Collaborative International Dictionary of English v.0.48:

Tasker \Task"er\, n.
   1. One who imposes a task.
      [1913 Webster]

   2. One who performs a task, as a day-laborer. [R.]
      [1913 Webster]

   3. A laborer who receives his wages in kind. [Scot.]
      [1913 Webster]