Perihelion (noun) - A point in the orbit of a planet, comet, or other celestial body that is closest to the Sun. Etymological Definition: From the Greek peri hélion meaning “near the Sun”.

Periastron (noun) - The point in the orbit of a binary star system that is closest to the other star. Etymological Definition: From the Greek peri astron meaning “near a star”.

Perigon: Actual Definition- A plane figure with at least three straight sides and angles, and typically five or more. Etymological Definition- Derived from the Greek root “peri-” meaning “around”.

Periodontal (adj.): "surrounding a tooth, pertaining to the lining membrane of the socket of a tooth," 1848, literally "around the tooth," from peri- "around" + Greek odon (genitive odontos) "tooth" (from PIE root *dent- "tooth").

periosteum (n.): "the enveloping membrane of the bones," 1590s, from Modern Latin periosteum, Late Latin periosteon, from Greek periosteon, neuter of periosteos "round the bones," from peri "around, about" (see peri-) + osteon "bone" (from PIE root *ost- "bone"). Related: Periosteal.

Peripeteia: Actual Definition- A sudden and unexpected change of fortune or reversal of circumstances, especially in a literary work. Etymological Definition- Derived from the Greek root “peri-” meaning “around”.

Peripatetic: Actual Definition- Moving or traveling from place to place, especially on foot. Etymological Definition- Derived from the Greek root “peri-” meaning “around”.

Periphery: Actual Definition- The outer limit or edge of something, especially a geographical area. Etymological Definition- Derived from the Greek root “peri-” meaning “around”.

Periphrasis: Actual Definition- The use of more words than necessary to express an idea, especially as a stylistic device. Etymological Definition- Derived from the Greek root “peri-” meaning “around”. [phrásis, “manner of expression.”]

Perigee (noun): the point in the orbit of the moon or a satellite at which it is nearest to the earth; Etymological Definition: derived from the Greek word “perigē” which means “around the earth”.

Periphrasis (noun): a roundabout or indirect manner of speaking or writing; Etymological Definition: derived from the Greek word “periphrasis” which means “circumlocution”.

Peripeteia (noun): a sudden and unexpected reversal of fortune or situation; Etymological Definition: derived from the Greek word “peripeteia” which means “around the feet”.

Periaktoi (noun): a triangular revolving stage device; Etymological Definition: derived from the Greek word “periaktos” which means “roundabout”.

Peripateticism (noun): the philosophy or practice of engaging in philosophical dialogue while walking; Etymological Definition: derived from the Greek word “peripatetikos” which means “to walk about”.