The Collaborative International Dictionary of English v.0.48:

Seminal \Sem"i*nal\, a. [L. seminalis, fr. semen, seminis, seed,
   akin to serere to sow: cf. F. seminal. See Sow to scatter
   seed.]
   1. Pertaining to, containing, or consisting of, seed or
      semen; as, the seminal fluid.
      [1913 Webster]

   2. Contained in seed.
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   3. Hence: Holding the first place in a series of developed
      results or consequents; serving as a source, or first
      principle; giving rise to related ideas or results;
      germinal; radical; primary; original; as, seminal
      principles of generation; seminal virtue; a seminal
      discovery.
      [1913 Webster +PJC]

            The idea of God is, beyond all question or
            comparison, the one great seminal principle. --Hare.
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   Seminal leaf (Bot.), a seed leaf, or cotyleden.

   Seminal receptacle. (Zool.) Same as Spermatheca.
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The Collaborative International Dictionary of English v.0.48:

Seminal \Sem"i*nal\, n.
   A seed. [Obs.] --Sir T. Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

seminal
    adj 1: pertaining to or containing or consisting of semen;
           "seminal fluid"
    2: containing seeds of later development; "seminal ideas of one
       discipline can influence the growth of another" [syn:
       germinal, originative, seminal]