Definition from Wiktionary, the free dictionary
Devonian (not comparable)
- (geology) of a geologic period within the Paleozoic era; comprises lower, middle and upper epochs from about 415 to 360 million years ago
- (chiefly dated) Of or pertaining to the English region of Devon.
Devonian (plural Devonians)
Proper noun 
- (geology) the Devonian period