sem·i·nal 
(sĕmə-nəl)
(sĕmə-nəl)adj.
1. Of, relating to, containing, or conveying semen or seed.
2. Of, relating to, or having the power to originate; creative.
3. Highly influential in an original way; constituting or providing a basis for further development: a seminal idea in the creation of a new theory.
[Middle English, from Old French, from Latin sēminālis, from sēmen, sēmin-, seed; see SEMEN.]
semi·nal·ly adv.