Source : Webster's Revised Unabridged Dictionary (1913)

Observation \Ob`ser*va"tion\, n. [L. observatio: cf.F.
   observation.]
   1. The act or the faculty of observing or taking notice; the
      act of seeing, or of fixing the mind upon, anything.

            My observation, which very seldom lies. --Shak.

   2. The result of an act, or of acts, of observing; view;
      reflection; conclusion; judgment.

            In matters of human prudence, we shall find the
            greatest advantage in making wise observations on
            our conduct.                          --I. Watts.

   3. Hence: An expression of an opinion or judgment upon what
      one has observed; a remark. ``That's a foolish
      observation.'' --Shak.

            To observations which ourselves we make We grow more
            partial for the observer's sake.      --Pope.

   4. Performance of what is prescribed; adherence in practice;
      observance. [Obs.]

            We are to procure dispensation or leave to omit the
            observation of it in such circumstances. --Jer.
                                                  Taylor.

   5. (Science)
      (a) The act of recognizing and noting some fact or
          occurrence in nature, as an aurora, a corona, or the
          structure of an animal.
      (b) Specifically, the act of measuring, with suitable
          instruments, some magnitude, as the time of an
          occultation, with a clock; the right ascension of a
          star, with a transit instrument and clock; the sun's
          altitude, or the distance of the moon from a star,
          with a sextant; the temperature, with a thermometer,
          etc.
      (c) The information so acquired.

   Note: When a phenomenon is scrutinized as it occurs in
         nature, the act is termed an observation. When the
         conditions under which the phenomenon occurs are
         artificial, or arranged beforehand by the observer, the
         process is called an experiment. Experiment includes
         observation.

   {To take an observation} (Naut.), to ascertain the altitude
      of a heavenly body, with a view to fixing a vessel's
      position at sea.

   Syn: Observance; notice; attention; remark; comment; note.
        See {Observance}.

Source : WordNet®

observation
     n 1: the act of making and recording a measurement
     2: the act of observing; taking a patient look [syn: {observance},
         {watching}]
     3: facts learned by observing; "he reported his observations to
        the mayor"
     4: the act of noticing or paying attention; "he escaped the
        notice of the police" [syn: {notice}, {observance}]
     5: a remark expressing careful consideration [syn: {reflection},
         {reflexion}]