Devonian (adj.)

1610s, "of or pertaining to Devonshire;" see Devon + -ian. The earlier adjective was Devonish (early 14c.). In reference to a geological era, 1837, applied by Murchison, because the formations of that age are prominent in the county, where they first were studied.

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Definitions of Devonian from WordNet

Devonian (n.)
from 405 million to 345 million years ago; preponderance of fishes and appearance of amphibians and ammonites;
Synonyms: Devonian period / Age of Fishes