in Astronomy, the time occupied by a star or planet in making a revolution round the sun, or the duration of its course till it return to the same part of its orbit. See Astronomy.

Music. See the article Music.

Chronology, denotes a revolution of a certain number of years, or a series of years, by which, in different nations, and on different occasions, time is measured. See Chronology.

Grammar, denotes a small compass of discourse, containing a perfect sentence, and distinguished at the end by a point or full stop. Father Buffier observes that there are two difficulties in the use of the period or point; first, in distinguishing it from the colon or double point; and, secondly, in determining justly the end of a period or perfect sentence. It may be remarked, that the supernumerary members of a period, separated from the rest by colons and semicolons, usually commence with a conjunction; yet it is true that sometimes these conjunctions rather begin new periods than supernumerary members of a preceding one. It is the sense of things, and the author's own discretion, that must make the proper distinction in such cases. No rules will be of any service unless this be admitted as one, that when that which follows the conjunction is of as great extent as that which precedes it, it is usually a new period, but otherwise not. The second difficulty arises from this, that the sense appears to be perfect in several short detached phrases, in which it does not seem there should be periods. This is frequent in free discourse, as, We are all in suspense, make your proposals immediately, you will be to blame for detaining us longer. Here it is evident that simple phrases have each a perfect sense like periods, and ought to be marked accordingly; but that the shortness of the discourse making them easily comprehended, the pointing is neglected. De Colonia defines a period a short but perfect sentence, consisting of certain parts or members depending one upon another, and connected together by some common vinculum. According to the celebrated definition of Aristotle, a period is a discourse which has a beginning, a middle, and an end, all of them visible at one view. Rhetoricians, in treating of the structure of sentences, consider a period as one of the four parts of composition. The periods allowed in oratory are three: a period of two members, called by the Greeks dicolas, and by the Latins bimembri; a period of three members, called tricolos and trimembri; and a period of four, called quadrinembri and tetracolos.

numbers, is a distinction made by a point or comma, after every sixth place or figure, and used in numeration for the more readily distinguishing and naming of the several figures or places.

Medicine, is applied to certain diseases which have intervals and returns, to denote an entire course or cycle of such disease, or its progress from any state through all the rest, till it return to the same again.