Oxide. The combination of a metal with oxygen; rust is oxide of iron.
Oxygen. One of the constituent parts of the air of the atmosphere; that part which supports life. For a farther explanation of the word, consult elementary works on chemistry.
Pachydermata. An order of quadrupeds, including the elephant, rhinoceros, horse, pig, &c., distinguished by having thick skins. Etym., παχυς, pachus, thick, and δερμα, derma, skin, or hide.
Pachydermatous. Belonging to Pachydermata.
Palæotherium, Paleothere. A fossil extinct quadruped, belonging to the order Pachydermata, resembling a pig, or tapir, but of great size. Etym., παλαιος, palaios, ancient, and θηριον, therion, wild beast.
Paleontology. The science which treats of fossil remains, both animal and vegetable. Etym., παλαιος, palaios, ancient, οντα, onta, beings, and λογος, logos, a discourse.
Pelagian, Pelagic. Belonging to the deep sea. Etym., pelagus, sea.
Peperino. An Italian name for a particular kind of volcanic rock, formed like tuff, by the cementing together of volcanic sand, cinders, or scoriæ, &c.
Petroleum. A liquid mineral pitch, so called because it is seen to ooze like oil out of the rock. Etym., petra, rock, and oleum, oil.
Phænogamous or Phanerogamic Plants. A name given by Linnæus to those plants in which the reproductive organs are apparent. Etym., φανερος, phaneros, evident, or φαινω, phaino, to show, and γαμος, gamos, marriage.