The Collaborative International Dictionary of English v.0.48:

Patriarch \Pa"tri*arch\ (p[=a]"tr[i^]*[aum]rk), n. [F.
   patriarche, L. patriarcha, Gr. paria`rchhs, fr. paria`
   lineage, especially on the father's side, race; path`r father
   + 'archo`s a leader, chief, fr. 'a`rchein to lead, rule. See
   Father, Archaic.]
   1. The father and ruler of a family; one who governs his
      family or descendants by paternal right; -- usually
      applied to heads of families in ancient history,
      especially in Biblical and Jewish history to those who
      lived before the time of Moses.
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   2. (R. C. Ch. & Gr. Ch.) A dignitary superior to the order of
      archbishops; as, the patriarch of Constantinople, of
      Alexandria, or of Antioch.
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   3. A venerable old man; an elder. Also used figuratively.
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            The patriarch hoary, the sage of his kith and the
            hamlet.                               --Longfellow.
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            The monarch oak, the partiarch of trees. --Dryde.
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WordNet (r) 3.0 (2006):

patriarch
    n 1: title for the heads of the Eastern Orthodox Churches (in
         Istanbul and Alexandria and Moscow and Jerusalem)
    2: the male head of family or tribe [syn: patriarch,
       paterfamilias]
    3: any of the early biblical characters regarded as fathers of
       the human race
    4: a man who is older and higher in rank than yourself