Source : Webster's Revised Unabridged Dictionary (1913)

Observe \Ob*serve"\, v. i.
   1. To take notice; to give attention to what one sees or
      hears; to attend.

   2. To make a remark; to comment; -- generally with on or
      upon.

Observe \Ob*serve"\, v. t. [imp. & p. p. {Observed}; 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.

            Ye shall observe the feast of unleavened bread.
                                                  --Ex. xii. 17.

            He wolde no such cursedness observe.  --Chaucer.

            Must I budge? Must I observe you?     --Shak.

            With solemn purpose to observe Immutably his
            sovereign will.                       --Milton.

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

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

Source : WordNet®

observe
     v 1: discover or determine the existence, presence, or fact of;
          "She detected high levels of lead in her drinking
          water"; "We found traces of lead in the paint" [syn: {detect},
           {find}, {discover}, {notice}]
     2: make mention of; "She observed that his presentation took up
        too much time"; "They noted that it was a fine day to go
        sailing" [syn: {note}, {mention}, {remark}]
     3: observe with care or pay close attention to; "Take note of
        this chemical reaction" [syn: {note}, {take note}]
     4: watch attentively; "Please observe the reaction of these two
        chemicals"
     5: show respect towards; "honor your parents!" [syn: {respect},
         {honor}, {honour}, {abide by}] [ant: {disrespect}]
     6: celebrate, as of holidays or rites; "Keep the commandments";
        "celebrate Christmas"; "Observe Yom Kippur" [syn: {celebrate},
         {keep}]
     7: follow with the eyes or the mind; "Keep an eye on the baby,
        please!"; "The world is watching Sarajevo"; "She followed
        the men with the binoculars" [syn: {watch}, {follow}, {watch
        over}, {keep an eye on}]
     8: observe correctly or closely; "The pianist kept time with
        the metronome"; "keep count"; "I cannot keep track of all
        my employees" [syn: {keep}, {maintain}]
     9: conform one's action or practice to; "keep appointments";
        "she never keeps her promises"; "We kept to the original
        conditions of the contract" [syn: {keep}]