The Collaborative International Dictionary of English v.0.48:

Sinker \Sink"er\, n.
   One who, or that which, sinks. Specifically:
   (a) A weight on something, as on a fish line, to sink it.
   (b) In knitting machines, one of the thin plates, blades, or
       other devices, that depress the loops upon or between the
       needles.
       [1913 Webster]

   Dividing sinker, in knitting machines, a sinker between two
      jack sinkers and acting alternately with them.

   Jack sinker. See under Jack, n.

   Sinker bar.
   (a) In knitting machines, a bar to which one set of the
       sinkers is attached.
   (b) In deep well boring, a heavy bar forming a connection
       between the lifting rope and the boring tools, above the
       jars.
       [1913 Webster]

WordNet (r) 3.0 (2006):

sinker
    n 1: a small ring-shaped friedcake [syn: doughnut, donut,
         sinker]
    2: a weight that sinks (as to hold nets or fishing lines under
       water)
    3: a pitch that curves downward rapidly as it approaches the
       plate