Dictionary:

antepenultimate

  (ăn'tē-pĭ-nŭl'tə-mĭt)

Coming before the next to the last in a series.

An antepenult.

[From Late Latin antepaenultimus : Latin ante-, ante- + Latin paenultimus, next to last; see penult.]

Some words are just too good not to use. People looking up information about Clark Gable, whose birthday was not long ago, found an unexpected word treat:

"Gable's last film, 1961's The Misfits, was also the final film of Marilyn Monroe and the antepenultimate film of co-star Montgomery Clift."

Link: Clark Gable: Biography and Much More From Answers.com

Posted February 2, 2006.

See our Word Overheard blog to see interesting uses of strange words.

The noun has one meaning:

Meaning #1: the 3rd syllable of a word counting back from the end
  Synonym: antepenult

The adjective antepenultimate has one meaning:

Meaning #1: third from last