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

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "sinker":
   Brussels biscuit, Melba toast, apple fritter, beignet,
   beignet aux pommes, biscuit, bismarck, bob, bowl, cast,
   change of pace, change-up, chuck, chunk, cracker, cruller, curve,
   doughnut, downcurve, fastball, fastnacht, fling, flip,
   forward pass, friedcake, fritter, graham cracker, hardtack, heave,
   hurl, incurve, knuckleball, lateral, lateral pass, lead, lob,
   olykoek, outcurve, pass, peg, pilot biscuit, pitch, plumb, plummet,
   pretzel, put, raised doughnut, rusk, saltine, sandbag, screwball,
   sea biscuit, serve, service, ship biscuit, shot-put, shy, slider,
   sling, soda cracker, spitball, spitter, throw, toss, twister,
   upcurve, wafer, weight, zwieback