WordNet (r) 3.0 (2006):

sesquicentennial
    n 1: the 150th anniversary (or the celebration of it)

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "sesquicentennial":
   C, anniversary, annual holiday, bicentenary, bicentennial,
   biennial, birthday, bissextile day, cental, centare, centenarian,
   centenary, centennial, centennium, centigram, centimeter,
   centipede, centistere, centred, centref, centrev, centumvir,
   centumvirate, centurion, century, commemoration, cwt, decennial,
   diamond jubilee, golden wedding anniversary, gross, hecatomb,
   holy days, hundred, hundredweight, immovable feast, jubilee,
   leap year, long hundred, name day, natal day, octennial, one C,
   quadrennial, quasquicentennial, quincentenary, quincentennial,
   quinquennial, septennial, sesquicentenary, sextennial,
   silver wedding anniversary, tercentenary, tercentennial,
   tricennial, triennial, wedding anniversary