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.
      [1913 Webster]

   2. (R. C. Ch. & Gr. Ch.) A dignitary superior to the order of
      archbishops; as, the patriarch of Constantinople, of
      Alexandria, or of Antioch.
      [1913 Webster]

   3. A venerable old man; an elder. Also used figuratively.
      [1913 Webster]

            The patriarch hoary, the sage of his kith and the
            hamlet.                               --Longfellow.
      [1913 Webster]

            The monarch oak, the partiarch of trees. --Dryde.
      [1913 Webster]

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

Moby Thesaurus II by Grady Ward, 1.0:

166 Moby Thesaurus words for "patriarch":
   Aaronic priesthood, Father Time, Grand Penitentiary, Holy Father,
   Melchizedek priesthood, Methuselah, Nestor, Old Paar, Seventy,
   abba, abuna, ancestors, antecedents, antediluvian, antipope,
   antique, apostle, archbishop, archdeacon, architect, archpriest,
   ascendants, author, back number, bishop, bishop coadjutor, boss,
   bwana, canon, cardinal, cardinal bishop, cardinal deacon,
   cardinal priest, centenarian, chaplain, chef, chief,
   church dignitary, coadjutor, conservative, creator, curate, dad,
   daddy, deacon, dean, diocesan, dodo, dotard, ecclesiarch, elder,
   elders, employer, exarch, father, fathers, fogy, forebears,
   forefathers, fossil, foster father, founder, fud, fuddy-duddy,
   gaffer, geezer, generator, genitor, golden-ager, goodman, governor,
   gramps, grandfather, grandfathers, grandparents, grandsire, granny,
   graybeard, guru, has-been, hierarch, high priest, husband,
   inventor, liege, liege lord, longhair, lord, lord paramount, maker,
   master, matriarch, metropolitan, mid-Victorian, mossback,
   nonagenarian, octogenarian, old believer, old chap, old codger,
   old crock, old dodo, old dog, old duffer, old fogy, old geezer,
   old gent, old gentleman, old liner, old man, old party, old poop,
   old woman, old-timer, older, oldster, originator, overlord, pa,
   padrone, pantaloon, pap, papa, pappy, paramount, pater,
   paterfamilias, patriarchs, patron, penitentiary, pontiff, pop,
   pope, pops, prebendary, predecessors, prelate, presbyter, priest,
   primate, progenitors, rabbi, reactionary, rector, regular old fogy,
   relic, rural dean, sahib, seigneur, seignior, senior citizen,
   septuagenarian, sexagenarian, sire, square, starets, stepfather,
   subdean, suffragan, teacher, the old man, the quiet-voiced elders,
   traditionalist, venerable sir, veteran, vicar



Easton's 1897 Bible Dictionary:

Patriarch
   a name employed in the New Testament with reference to Abraham
   (Heb. 7:4), the sons of Jacob (Acts 7:8, 9), and to David
   (2:29). This name is generally applied to the progenitors of
   families or "heads of the fathers" (Josh. 14:1) mentioned in
   Scripture, and they are spoken of as antediluvian (from Adam to
   Noah) and post-diluvian (from Noah to Jacob) patriachs. But the
   expression "the patriarch," by way of eminence, is applied to
   the twelve sons of Jacob, or to Abraham, Isaac, and Jacob.

     "Patriachal longevity presents itself as one of the most
   striking of the facts concerning mankind which the early history
   of the Book of Genesis places before us...There is a large
   amount of consentient tradition to the effect that the life of
   man was originally far more prolonged than it is at present,
   extending to at least several hundred years. The Babylonians,
   Egyptians, and Chinese exaggerated these hundreds into
   thousands. The Greeks and Romans, with more moderation, limited
   human life within a thousand or eight hundred years. The Hindus
   still farther shortened the term. Their books taught that in the
   first age of the world man was free from diseases, and lived
   ordinarily four hundred years; in the second age the term of
   life was reduced from four hundred to three hundred; in the
   third it became two hundred; in the fourth and last it was
   brought down to one hundred" (Rawlinson's Historical
   Illustrations).