period (n.)

late Old English, the second book of the Old Testament, from Latin exodus, from Greek exodos "a military expedition; a solemn procession; departure; death," literally "a going out," from ex "out" (see ex-) + hodos "a way, path, road; a ride, journey, march," figuratively "way out, means," a word of uncertain origin. The book is so called because it tells of the departure of the Israelites from Egypt under the leadership of Moses. General sense (with lower-case -e-) "departure from a place," especially "the migration of large bodies of people or animals from one country or region to another," is from 1620s.

Beekes derives the Greek word from PIE *sod- "course" and says it is traditionally connected with Slavic words for "course" (such as Russian xod "course, progress," "which might have been borrowed from Iranian") and adds that it is perhaps also related to Sanskrit a-sad- "to tread on, go on," Avestan apa-had- "to go away; become weak," "but the relation between them is unclear, as is the connection to the PIE root *sed- "sit" (proposed in Watkins, etc.)."

punctuation mark, 1520s as a Latin word, nativized by 1590s, from Latin comma "short phrase or clause of a sentence or line of poetry," from Greek komma "clause in a sentence," also ""stamp, coinage," literally "piece which is cut off," from koptein "to strike, smite, cut off; disable, tire out," which is perhaps from PIE root *kop- "to beat, strike, smite" (see hatchet (n.)), or perhaps Pre-Greek.

Like colon (n.1) and period it was originally a Greek rhetorical term for a part of a sentence, and like them it has been transferred to the punctuation mark that identifies it. In reading aloud the punctuation mark is used to admit small interruptions in continuity of speech for the sake of clarity, but its purpose is to indicate grammatical structure.