Definition of "role"

In plants, the ability to recognize self from nonself plays an important role in fertilization, because self-fertilization will result in less diverse offspring than fertilization with pollen from another individual.

2013 May-June, Katrina G. Claw, “Rapid Evolution in Eggs and Sperm”, in American Scientist, volume 101, number 3

As students all over the United States knuckle down to learning, the rumble of war drums once more proclaims Mars high man in Europe. Discarding morbid curiosity, every student should consider it vitally necessary to get a general picture of the causes, movements, and possible effects of World War II. The average U. S. citizen's knowledge of World War II will probably decide his role in it.

1939 November 10, “Following The War”, in The Chart‎, volume I, number 1, Joplin, Missouri: Joplin Junior College, page 4, column 1

Examining these verbs one by one, what one finds is that Auxiliary Selection does correlate in the expected way with the two kinds of optional transitivity, confirming that with each predicate, one semantic role has a fixed link with initial 1-hood, another with initial 2-hood.

1984, David M. Perlmutter, Carol G. Rosen, Studies in relational grammar: Volume 2