NOUN (1)

1. someone who is at least 100 years old;


ADJECTIVE (1)

1. being at least 100 years old;

The Collaborative International Dictionary of English v.0.48:

Centenarian \Cen`te*na"ri*an\, a.
   Of or relating to a hundred years. -- n. A person a hundred
   years old.
   [1913 Webster]

WordNet (r) 3.0 (2006):

centenarian
    adj 1: being at least 100 years old
    n 1: someone who is at least 100 years old

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "centenarian":
   C, Father Time, Methuselah, Nestor, Old Paar, bicentenary,
   bicentennial, cental, centare, centenary, centennial, centennium,
   centigram, centimeter, centipede, centistere, centred, centref,
   centrev, centumvir, centumvirate, centurion, century, cwt, dotard,
   elder, gaffer, geezer, golden-ager, gramps, grandfather, grandsire,
   graybeard, gross, hecatomb, hundred, hundredweight, long hundred,
   nonagenarian, octogenarian, old chap, old codger, old dog,
   old duffer, old geezer, old gent, old gentleman, old man,
   old party, old-timer, older, oldster, one C, pantaloon, patriarch,
   presbyter, senior citizen, septuagenarian, sesquicentenary,
   sesquicentennial, sexagenarian, tercentenary, tercentennial,
   the quiet-voiced elders, venerable sir, veteran