4  definitions  found 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Parallax  \Par"al*lax\,  n.  [Gr.  ?  alternation,  the  mutual 
  inclination  of  two  lines  forming  an  angle,  fr  ?  to  change  a 
  little,  go  aside,  deviate;  ?  beside,  beyond  +  ?  to  change: 
  cf  F.  parallaxe.  Cf  {Parallel}.] 
  1.  The  apparent  displacement,  or  difference  of  position,  of 
  an  object,  as  seen  from  two  different  stations,  or  points 
  of  view. 
 
  2.  (Astron.)  The  apparent  difference  in  position  of  a  body 
  (as  the  sun,  or  a  star)  as  seen  from  some  point  on  the 
  earth's  surface,  and  as  seen  from  some  other  conventional 
  point,  as  the  earth's  center  or  the  sun. 
 
  {Annual  parallax},  the  greatest  value  of  the  heliocentric 
  parallax,  or  the  greatest  annual  apparent  change  of  place 
  of  a  body  as  seen  from  the  earth  and  sun;  as  the  annual 
  parallax  of  a  fixed  star. 
 
  {Binocular  parallax},  the  apparent  difference  in  position  of 
  an  object  as  seen  separately  by  one  eye,  and  then  by  the 
  other  the  head  remaining  unmoved. 
 
  {Diurnal},  or  {Geocentric},  {parallax},  the  parallax  of  a 
  body  with  reference  to  the  earth's  center.  This  is  the 
  kind  of  parallax  that  is  generally  understood  when  the 
  term  is  used  without  qualification. 
 
  {Heliocentric  parallax},  the  parallax  of  a  body  with 
  reference  to  the  sun,  or  the  angle  subtended  at  the  body 
  by  lines  drawn  from  it  to  the  earth  and  sun;  as  the 
  heliocentric  parallax  of  a  planet. 
 
  {Horizontal  parallax},  the  geocentric  parallx  of  a  heavenly 
  body  when  in  the  horizon,  or  the  angle  subtended  at  the 
  body  by  the  earth's  radius. 
 
  {Optical  parallax},  the  apparent  displacement  in  position 
  undergone  by  an  object  when  viewed  by  either  eye  singly. 
  --Brande  &  C. 
 
  {Parallax  of  the  cross  wires}  (of  an  optical  instrument), 
  their  apparent  displacement  when  the  eye  changes  its 
  position,  caused  by  their  not  being  exactly  in  the  focus 
  of  the  object  glass. 
 
  {Stellar  parallax},  the  annual  parallax  of  a  fixed  star. 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Diurnal  \Di*ur"nal\,  a.  [L.  diurnalis,  fr  dies  day  See 
  {Deity},  and  cf  {Journal}.] 
  1.  Relating  to  the  daytime;  belonging  to  the  period  of 
  daylight,  distinguished  from  the  night;  --  opposed  to 
  {nocturnal};  as  diurnal  heat;  diurnal  hours. 
 
  2.  Daily;  recurring  every  day  performed  in  a  day  going 
  through  its  changes  in  a  day  constituting  the  measure  of 
  a  day  as  a  diurnal  fever;  a  diurnal  task;  diurnal 
  aberration,  or  diurnal  parallax;  the  diurnal  revolution  of 
  the  earth. 
 
  Ere  twice  the  horses  of  the  sun  shall  bring  Their 
  fiery  torcher  his  diurnal  ring.  --Shak. 
 
  3.  (Bot.)  Opening  during  the  day  and  closing  at  night;  -- 
  said  of  flowers  or  leaves. 
 
  4.  (Zo["o]l.)  Active  by  day  --  applied  especially  to  the 
  eagles  and  hawks  among  raptorial  birds,  and  to  butterflies 
  (Diurna)  among  insects. 
 
  {Diurnal  aberration}  (Anat.),  the  aberration  of  light  arising 
  from  the  effect  of  the  earth's  rotation  upon  the  apparent 
  direction  of  motion  of  light. 
 
  {Diurnal  arc},  the  arc  described  by  the  sun  during  the 
  daytime  or  while  above  the  horizon;  hence  the  arc 
  described  by  the  moon  or  a  star  from  rising  to  setting. 
 
  {Diurnal  circle},  the  apparent  circle  described  by  a 
  celestial  body  in  consequence  of  the  earth's  rotation. 
 
  {Diurnal  motion  of  the  earth},  the  motion  of  the  earth  upon 
  its  axis  which  is  described  in  twenty-four  hours. 
 
  {Diurnal  motion  of  a  heavenly  body},  that  apparent  motion  of 
  the  heavenly  body  which  is  due  to  the  earth's  diurnal 
  motion. 
 
  {Diurnal  parallax}.  See  under  {Parallax}. 
 
  {Diurnal  revolution  of  a  planet},  the  motion  of  the  planet 
  upon  its  own  axis  which  constitutes  one  complete 
  revolution. 
 
  Syn:  See  {Daily}. 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Diurnal  \Di*ur"nal\,  n.  [Cf.  F.  diurnal  a  prayerbook.  See 
  {Diurnal},  a.] 
  1.  A  daybook;  a  journal.  [Obs.]  --Tatler. 
 
  2.  (R.  C.  Ch.)  A  small  volume  containing  the  daily  service 
  for  the  ``little  hours,''  viz.,  prime,  tierce,  sext, 
  nones,  vespers,  and  compline. 
 
  3.  (Zo["o]l.)  A  diurnal  bird  or  insect. 
 
  From  WordNet  r  1.6  [wn]: 
 
  diurnal 
  adj  1:  (biology)  belonging  to  or  active  during  the  day  "diurnal 
  animals  are  active  during  the  day";  "diurnal  flowers 
  are  open  during  the  day  and  closed  at  night"  [ant:  {nocturnal}] 
  2:  having  a  daily  cycle  or  occurring  every  day  "diurnal 
  rhythms";  "diurnal  rotation  of  the  heavens";  "the  diurnal 
  slumber  of  bats" 

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