The Collaborative International Dictionary of English v.0.48:

Constantinople \Constantinople\ prop. n.
   the former capital of the Eastern Roman Empire; it was built
   on the site of ancient Byzantium, and the name was changed to
   Istanbul by the Turks.

   Syn: Istanbul, Stambul, Stamboul.
        [WordNet 1.5]

   Note: The name change was the subject of a humorous song in
         the 1950's "Istanbul (not Constantinople)":
         Artists: The Four Lads -- peak Billboard position # 10
         in 1953 -- Words by Jimmy Kennedy and Music by Nat
         Simon -- (C) Chappell & Co. Istanbul was Constantinople
         Now it's Istanbul, not Constantinople Been a long time
         gone, Constantinople Now it's Turkish delight on a
         moonlit night Every gal in Constantinople Lives in
         Istanbul, not Constantinople So if you've a date in
         Constantinople She'll be waiting in Istanbul Even old
         New York Was once New Amsterdam Why they changed it I
         can't say People just liked it better that way Take me
         back to Constantinople No, you can't go back to
         Constantinople Now it's Istanbul, not Constantinople
         Why did Constantinople get the works? That's nobody's
         business but the Turks'
         [PJC]

WordNet (r) 3.0 (2006):

Constantinople
    n 1: the largest city and former capital of Turkey; rebuilt on
         the site of ancient Byzantium by Constantine I in the
         fourth century; renamed Constantinople by Constantine who
         made it the capital of the Byzantine Empire; now the seat
         of the Eastern Orthodox Church [syn: Istanbul, Stambul,
         Stamboul, Constantinople]
    2: the council in 869 that condemned Photius who had become the
       patriarch of Constantinople without approval from the
       Vatican, thereby precipitating the schism between the eastern
       and western churches [syn: Constantinople, Fourth Council
       of Constantinople]
    3: the sixth ecumenical council in 680-681 which condemned
       Monothelitism by defining two wills in Christ, divine and
       human [syn: Constantinople, Third Council of
       Constantinople]
    4: the fifth ecumenical council in 553 which held Origen's
       writings to be heretic [syn: Constantinople, Second
       Council of Constantinople]
    5: the second ecumenical council in 381 which added wording
       about the Holy Spirit to the Nicene Creed [syn:
       Constantinople, First Council of Constantinople]