The Collaborative International Dictionary of English v.0.48:

Rod \Rod\, n. [The same word as rood. See Rood.]
   1. A straight and slender stick; a wand; hence, any slender
      bar, as of wood or metal (applied to various purposes).
      Specifically:
      (a) An instrument of punishment or correction;
          figuratively, chastisement.
          [1913 Webster]

                He that spareth his rod hateth his son. --Prov.
                                                  xiii. 24.
          [1913 Webster]
      (b) A kind of sceptor, or badge of office; hence,
          figuratively, power; authority; tyranny; oppression.
          "The rod, and bird of peace." --Shak.
      (c) A support for a fishing line; a fish pole. --Gay.
      (d) (Mach. & Structure) A member used in tension, as for
          sustaining a suspended weight, or in tension and
          compression, as for transmitting reciprocating motion,
          etc.; a connecting bar.
      (e) An instrument for measuring.
          [1913 Webster]

   2. A measure of length containing sixteen and a half feet; --
      called also perch, and pole.
      [1913 Webster]

   Black rod. See in the Vocabulary.

   Rods and cones (Anat.), the elongated cells or elements of
      the sensory layer of the retina, some of which are
      cylindrical, others somewhat conical.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rod
    n 1: a long thin implement made of metal or wood
    2: any rod-shaped bacterium
    3: a linear measure of 16.5 feet [syn: perch, rod, pole]
    4: a square rod of land [syn: perch, rod, pole]
    5: a visual receptor cell that is sensitive to dim light [syn:
       rod, rod cell, retinal rod]
    6: a gangster's pistol [syn: gat, rod]

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "rod":
   Maypole, atomic pile, automatic, bar, baton, billet, birch,
   blowgun, blowpipe, breeder reactor, bricks, caduceus, cane,
   cap of dignity, cap of maintenance, castigation, chain of office,
   chain reactor, chain-reacting pile, chastisement, club, coronet,
   correction, crook, crosier, cross-staff, crown, diadem, discipline,
   ermine, fasces, fast pile, ferule, firearm, flagstaff,
   flamethrower, furnace, gat, gavel, great seal, gun, handgun,
   heater, heterogeneous reactor, homogeneous reactor, ingot,
   intermediate pile, lattice, mace, mantle, musket, neutron factory,
   nuclear furnace, orb, paddle, pandybat, peashooter, piece, pile,
   pistol, plutonium reactor, pole, portfolio, power reactor,
   power-breeder reactor, privy seal, province, punition, purple,
   purple pall, radioactive waste, rattan, reactor, reactor pile,
   regalia, repeater, revolver, rifle, robe of state, rod of empire,
   rod of office, rods, royal crown, ruler, sawed-off shotgun, scape,
   scepter, seal, shaft, shooting iron, shotgun, signet, six-gun,
   six-shooter, slab, slow pile, staff, stalk, stellarator, stem,
   stick, strip, switch, tiara, tongue, totem pole, triple plume,
   truncheon, uraeus, uranium reactor, wand, wand of office



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

ROD
       Rewritable Optical Disk (OD)


Bouvier's Law Dictionary, Revised 6th Ed (1856):

ROD. A measure sixteen feet and a half long; a perch.