The Collaborative International Dictionary of English v.0.48:

Primeval \Pri*me"val\, a. [L. primaevus; primus first + aevum
   age. See Prime, a., and Age.]
   Belonging to the first ages; pristine; original; primitive;
   primary; as, the primeval innocence of man. "This is the
   forest primeval." --Longfellow.
   [1913 Webster]

         From chaos, and primeval darkness, came Light. --Keats.
   [1913 Webster]

WordNet (r) 3.0 (2006):

primeval
    adj 1: having existed from the beginning; in an earliest or
           original stage or state; "aboriginal forests"; "primal
           eras before the appearance of life on earth"; "the forest
           primeval"; "primordial matter"; "primordial forms of
           life" [syn: aboriginal, primal, primeval,
           primaeval, primordial]

Moby Thesaurus II by Grady Ward, 1.0:

90 Moby Thesaurus words for "primeval":
   abecedarian, aboriginal, ancestral, ancient, antenatal,
   antepatriarchal, atavistic, autochthonous, basal, basic, beginning,
   budding, central, creative, crucial, early, elemental, elementary,
   embryonic, erstwhile, fetal, fore, formative, former, foundational,
   fundamental, generative, genetic, germinal, gestatory, humanoid,
   immemorial, in embryo, in its infancy, in ovo, in the bud,
   inaugural, inceptive, inchoate, inchoative, incipient, incunabular,
   infant, infantile, initial, initiative, initiatory, introductory,
   inventive, late, nascent, natal, old, olden, once, onetime,
   original, parturient, past, patriarchal, postnatal, preadamite,
   preglacial, pregnant, prehistoric, prehuman, prenatal, previous,
   primal, primary, prime, primitive, primogenial, primoprimitive,
   primordial, prior, pristine, procreative, protogenic,
   protohistoric, protohuman, quondam, radical, recent, rudimental,
   rudimentary, seminal, sometime, then, ur