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PER-I-HEL-ION, or PER-I-HE'LI-UM, n. [G. περι, about, and ἡλιος, the sun.]

That part of the or bit of a planet or comet, in which it is at its least distance from the sun; opposed to aphelion. Encyc.

PER-I-HEX-A-HE'DRAL, a. [Gr. περι, and hexahedral.]

Designating a crystal whose primitive form is a four-sided prism, and in the secondary form is converted into a prism of six sides. – Cleaveland.

PER'IL, n. [Fr.; It. periglio; Sp. peligro; Port. perigo; from L. periculum, from Gr. πειραω, to try, to attempt, that is, to strain; πειρα, an attempt, danger, hazard; allied to πειρω, to pass, to thrust in or transfix; πειρα, is also the point or edge of a sword, coinciding with W. ber and pêr, a spit, a spear or pike. Hence L. experior, Eng. experience. The Greek πειραω is expressed in Dutch by vaaren, to go, to sail, to fare; gevaar, danger, peril; G. gefahr, from fahren. These words are all of one family. See Pirate. The primary sense of peril is an advance, a pushing or going forward; the radical sense of boldness. The Welsh has perig, perilous, from pêr, and peri, to bid or command, the root of L. impero, from the same root.]

  1. Danger; risk; hazard; jeopardy; particular exposure of person or property to injury, loss or destruction from any cause whatever. In perils of waters; in perils of robbers. – 2 Cor. xi.
  2. Danger denounced; particular exposure. You do it at your peril, or at the peril of your father's displeasure.

PER'IL, v.i.

To be in danger. – Milton.

PERIL, v.t.

To hazard; to risk; to expose to danger.

PER'IL-ED, pp.

Exposed to danger or loss.

PER'IL-ING, ppr.

Hazarding; risking.

PER'IL-OUS, a. [Fr. perileux.]

  1. Dangerous; hazardous; full of risk; as, a perilous undertaking; a perilous situation.
  2. Vulgarly used for very, like mighty; as, perilous shrewd. [Obs.] – Hudibras.
  3. Smart; witty; as, a perilous [parlous] boy. [Vulgar and obsolete.]


Dangerously; with hazard.


Dangerousness; danger; hazard.

PE-RIM'E-TER, n. [Gr. περι, about, and μετρον, measure.]

In geometry, the bounds and limits of a body or figure, or the sum of all the sides. The perimeters of surfaces or figures are lines; those of bodies are surfaces. In circular figures, instead of perimeter, we use circumference or periphery. – Encyc.

PER-INTERIM, adv. [Per interim; L.]

In the mean time.

PER-I-OC-TA-HE'DRAL, a. [Gr. περι and octahedral.]

Designating a crystal whose primitive form is a four-sided prism, and in its secondary form is converted into a prism of eight sides.

PE'RI-OD, n. [L. periodus; Fr. periode; It. Sp. and Port. periodo; Gr. περιοδος; περι, about, and ὁδος, way.]

  1. Properly, a circuit; hence, the time which is taken up by a planet in making its revolution round the sun, or the duration of its course till it returns to the point of its orbit where it began. Thus the period of the earth or its annual revolution is 365 days, 6 hours, 9 minutes, and 30 seconds. – Encyc.
  2. In chronology, a stated number of years; a revolution or series of years by which time is measured; as, the Calippic period; the Dionysian period; the Julian period.
  3. Any series of years or of days in which a revolution is completed, and the same course is to be begun.
  4. Any specified portion of time, designated by years, months, days or hours complete as, a period of a thousand years; the period of a year; the period of a day.
  5. End; conclusion. Death puts a period to a state of probation.
  6. An indefinite portion of any continued state, existence or series of events; as, the first period of life; the last period of a king's reign; the early periods of history.
  7. State at which any thing terminates; limit.
  8. Length or usual length of duration. Some experiments would be made how by art to make plants more tasting than their ordinary period. – Bacon.
  9. A complete sentence from one full stop to another. Periods are beautiful when they are not too long. – B. Jonson.
  10. The point that marks the end of a complete sentence; a full stop, thus ( . ).
  11. In numbers, a distinction made by a point or comma after every sixth place or figure. – Encyc.
  12. In medicine, the time of the exacerbation and remission of a disease, or of the paroxysm and intermission. Encyc. Julian period, in chronology, a period of 7980 years; a number produced by multiplying 23, the years of the solar cycle, into 19, the years of the lunar cycle, and their product by 15, the years of the Roman indiction.

PE'RI-OD, v.t.

To put an end to. [Not used.] – Shak.

PE-RI-OD'IC, or PE-RI-OD'IC-AL, a. [It. periodico; Fr. periodique.]

  1. Performed in a circuit, or in a regular revolution in a certain time, or in a series of successive circuits; as, the periodical motion of the planets round the sun; the periodical motion of the moon round the earth. – Watts.
  2. Happening by revolution, at a stated time; as, the conjunction of the sun and moon is periodical.
  3. Happening or returning regularly in a certain period of time. The Olympiads among the Greeks were periodical, as was the jubilee of the Jews.
  4. Performing some action at a stated time; as, the periodical fountains in Switzerland, which issue only at a particular hour of the day. – Addison.
  5. Pertaining to a period; constituting a complete sentence. – Adam's Lect.
  6. Pertaining to a revolution or regular circuit. – Brown.


A magazine or other publication, that is published at stated or regular periods.


One who publishes a periodical.


At stated periods; as, a festival celebrated periodically.


The state of having regular periods in changes or conditions. – Whewell.

PER-I-OS'TE-UM, n. [Gr. περι, about, and οστεον, bone.]

A nervous vascular membrane endued with quick sensibility, immediately investing the bones of animals. – Encyc. Coxe. The periosteum has very little sensibility in a sound state, but in some cases of disease it appears to be very sensible. – Wistar.

PER-I-PA-TET'IC, a. [Gr. περιπατητικος, from περιπατεω, to walk about; περι and πατεω.]

Pertaining to Aristotle's system of philosophy, or to the sect of his followers.


  1. A follower of Aristotle, so called because the founders of his philosophy taught, or his followers disputed questions, walking in the Lyceum at Athens. – Encyc.
  2. It is ludicrously applied to one who is obliged to walk, or cannot afford to ride. – Tatler.


The notions or philosophical system of Aristotle and his followers. – Barrow.


Peripheric. – Fleming.