The Collaborative International Dictionary of English v.0.48:

Log \Log\, n. [Icel. l[=a]g a felled tree, log; akin to E. lie.
   See Lie to lie prostrate.]
   1. A bulky piece of wood which has not been shaped by hewing
      or sawing.
      [1913 Webster]

   2. [Prob. the same word as in sense 1; cf. LG. log, lock,
      Dan. log, Sw. logg.] (Naut.) An apparatus for measuring
      the rate of a ship's motion through the water.
      [1913 Webster]

   Note: The common log consists of the log-chip, or logship,
         often exclusively called the log, and the log line, the
         former being commonly a thin wooden quadrant of five or
         six inches radius, loaded with lead on the arc to make
         it float with the point up. It is attached to the log
         line by cords from each corner. This line is divided
         into equal spaces, called knots, each bearing the same
         proportion to a mile that half a minute does to an
         hour. The line is wound on a reel which is so held as
         to let it run off freely. When the log is thrown, the
         log-chip is kept by the water from being drawn forward,
         and the speed of the ship is shown by the number of
         knots run out in half a minute. There are improved
         logs, consisting of a piece of mechanism which, being
         towed astern, shows the distance actually gone through
         by the ship, by means of the revolutions of a fly,
         which are registered on a dial plate.
         [1913 Webster]

   3. Hence: The record of the rate of speed of a ship or
      airplane, and of the course of its progress for the
      duration of a voyage; also, the full nautical record of a
      ship's cruise or voyage; a log slate; a log book.
      [1913 Webster +PJC]

   4. Hence, generally: A record and tabulated statement of the
      person(s) operating, operations performed, resources
      consumed, and the work done by any machine, device, or
      system.
      [1913 Webster +PJC]

   5. (Mining) A weight or block near the free end of a hoisting
      rope to prevent it from being drawn through the sheave.
      [1913 Webster]

   6. (computers) A record of activities performed within a
      program, or changes in a database or file on a computer,
      and typically kept as a file in the computer.
      [PJC]

   Log board (Naut.), a board consisting of two parts shutting
      together like a book, with columns in which are entered
      the direction of the wind, course of the ship, etc.,
      during each hour of the day and night. These entries are
      transferred to the log book. A folding slate is now used
      instead.

   Log book, or Logbook (Naut.),
      (a) a book in which is entered the daily progress of a
          ship at sea, as indicated by the log, with notes on
          the weather and incidents of the voyage; the contents
          of the log board.
      (b) a book in which a log[4] is recorded.

   Log cabin, Log house, a cabin or house made of logs.

   Log canoe, a canoe made by shaping and hollowing out a
      single log; a dugout canoe.

   Log glass (Naut.), a small sandglass used to time the
      running out of the log line.

   Log line (Naut.), a line or cord about a hundred and fifty
      fathoms long, fastened to the log-chip. See Note under 2d
      Log, n., 2.

   Log perch (Zool.), an ethiostomoid fish, or darter
      (Percina caprodes); -- called also hogfish and
      rockfish.

   Log reel (Naut.), the reel on which the log line is wound.


   Log slate. (Naut.) See Log board (above).

   Rough log (Naut.), a first draught of a record of the
      cruise or voyage.

   Smooth log (Naut.), a clean copy of the rough log. In the
      case of naval vessels this copy is forwarded to the proper
      officer of the government.

   To heave the log (Naut.), to cast the log-chip into the
      water; also, the whole process of ascertaining a vessel's
      speed by the log.
      [1913 Webster]