Pennsylvanian /ˌpɛn.sɪlˈveɪ.ni.ən/adjective 2noun 1forms 1 adjective2 •Of or pertaining to the state of Pennsylvania. •Of any of the three geologic epochs (lower, middle and upper) within the Carboniferous period from 318 to 299 million years ago; marked by a high oxygen atmosphere and the rise of reptiles and winged insects. noun1 •A native or resident of the state of Pennsylvania in the United States of America. formsPennsylvanians