The Collaborative International Dictionary of English v.0.48:

Patriarchal \Pa`tri*ar"chal\, a. [Cf. F. patriarcal.]
   1. Of or pertaining to a patriarch or to patriarchs;
      possessed by, or subject to, patriarchs; as, patriarchal
      authority or jurisdiction; a patriarchal see; a
      patriarchal church.
      [1913 Webster]

   2. Characteristic of a patriarch; venerable.
      [1913 Webster]

            About whose patriarchal knee
            Late the little children clung.       --Tennyson.
      [1913 Webster]

   3. (Ethnol.) Having an organization of society and government
      in which the head of the family exercises authority over
      all its generations.
      [1913 Webster]

   Patriarchal cross (Her.), a cross, the shaft of which is
      intersected by two transverse beams, the upper one being
      the smaller. See Illust. (2) of Cross.

   Patriarchal dispensation, the divine dispensation under
      which the patriarchs lived before the law given by Moses.
      [1913 Webster]

WordNet (r) 3.0 (2006):

patriarchal
    adj 1: characteristic of a form of social organization in which
           the male is the family head and title is traced through
           the male line [ant: matriarchal]
    2: relating to or characteristic of a man who is older or higher
       in rank

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "patriarchal":
   aboriginal, absolute, advanced, advanced in life,
   advanced in years, aged, along in years, ancestorial, ancestral,
   ancient, antepatriarchal, aristocratic, atavistic, authoritarian,
   autochthonous, autocratic, autonomous, bureaucratic, civic, civil,
   constitutional, democratic, despotic, dictatorial, elderly,
   fascist, fatherlike, fatherly, federal, federalist, federalistic,
   governmental, grandfatherly, grandmotherly, grandparental, gray,
   gray with age, gray-haired, gray-headed, grown old, gubernatorial,
   heteronomous, hoar, hoary, humanoid, maternal, matriarchal,
   matriarchic, monarchal, monarchial, monarchic, monocratic, mother,
   motherlike, motherly, official, old, old as Methuselah, oligarchal,
   oligarchic, parent, parental, parliamentarian, parliamentary,
   paternal, patriarchic, pluralistic, political, preadamite,
   preglacial, prehistoric, prehuman, prime, primeval, primitive,
   primogenial, primoprimitive, primordial, pristine, protohistoric,
   protohuman, republican, revered, reverend, reverential,
   self-governing, senectuous, theocratic, totalitarian, venerable,
   white, white with age, white-bearded, white-crowned, white-haired,
   wrinkled, wrinkly, years old