The Collaborative International Dictionary of English v.0.48:

Observe \Ob*serve"\ ([o^]b*z[~e]rv"), v. t. [imp. & p. p.
   Observed ([o^]b*z[~e]rvd"); p. pr. & vb. n. Observing.]
   [L. observare, observatum; ob (see Ob-) + servare to save,
   preserve, keep, heed, observe: cf. F. observer. See Serve.]
   1. To take notice of by appropriate conduct; to conform one's
      action or practice to; to keep; to heed; to obey; to
      comply with; as, to observe rules or commands; to observe
      civility.
      [1913 Webster]

            Ye shall observe the feast of unleavened bread.
                                                  --Ex. xii. 17.
      [1913 Webster]

            He wolde no such cursedness observe.  --Chaucer.
      [1913 Webster]

            Must I budge? Must I observe you?     --Shak.
      [1913 Webster]

            With solemn purpose to observe
            Immutably his sovereign will.         --Milton.
      [1913 Webster]

   2. To be on the watch respecting; to pay attention to; to
      notice with care; to see; to perceive; to notice; to
      discover; as, to observe an eclipse; to observe the color
      or fashion of a dress; to observe the movements of an
      army; to observe an accident.
      [1913 Webster +PJC]

   3. To express as what has been noticed; to utter as a remark;
      to say in a casual or incidental way; to remark.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

observed \observed\ adj.
   1. perceived with the eyes and sometimes with other senses;
      as, no explanation for the observed phenomena.
      [WordNet 1.5]

   2. Detected by systematic scientific observation; as,
      variation in the observed flux may depend on a number of
      factors.

   Syn: ascertained.
        [WordNet 1.5]

   3. Perceived directly with the eyes; observed at first hand.

   Syn: seen, witnessed.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

observed
    adj 1: discovered or determined by scientific observation;
           "variation in the ascertained flux depends on a number of
           factors"; "the discovered behavior norms"; "discovered
           differences in achievement"; "no explanation for the
           observed phenomena" [syn: ascertained, discovered,
           observed]