time

forever

עולם · נצח · סלה · ועד · עד

Bottom line

Olam is a very long but bounded span: for all time, and in a legal context often "until the Yovel," not literally forever. Netzach, selah, and va'ed are, on the Maharsha's reading of Eruvin 54a, the truly unbounded words: forever, everlasting, for all eternity. That reading is not the only one: ibn Saruk and Rabbi Yosef Kimchi treat all four as flat synonyms, and Rabbi Avraham ben Ezriel of Vienna limits the Gemara's finding to the verses where these words stand beside olam. The trap is le'olam: Rashi to Shemos 21:6 caps it at the fifty-year Yovel cycle, and the Maharsha builds on that, so a translator who writes "forever" for le'olam in a halachic pasuk has overshot. When olam stands beside one of the other three, the second word is doing work; do not collapse the pair into one English "forever."

Distinctions

olam (עולם)

Root ע-ל-ם. Rashi to Shemos 21:6: the pierced bondsman serves le'olam, meaning only to the Yovel, not without limit. Maharsha therefore reads olam as a long period that nonetheless ends, which is why the pairing in Eruvin 54a is not redundant. Rabbi Yaakov Tzvi Mecklenburg ties olam to al, "above": all of space and time is the field on which each creature strives to rise above where it stands, and Yovel is called le'olam because in it the slave rises to his master's free status. Rabbi Shlomo Pappenheim reads ne'elam, "hidden," from the same al: what is above one's range of perception is hidden from him.

netzach (נצח)

Root נ-צ-ח. Rabbi Shlomo Aharon Wertheimer: netzach is the continuous, unchanging permanence, a state that never alters. Mecklenburg derives it from tzach, "pristine, pure," the final state of being the soul reaches for.

selah (סלה)

Root ס-ל-ה. Two readings, and they are not reconcilable on the surface. (1) Eruvin 54a, followed by Rashi, Meiri and other classical meforshim to Tehillim 3:3: selah means forever, denoting what continues without end. The earliest translations of Tanach render it so consistently: Targum Yonasan in Aramaic, Aquilas in Greek, and the Peshitta in Syriac. Wertheimer sharpens it to the continual, the ever-repeating, as against netzach's continuous. (2) Radak (to Tehillim 3:3 and in Sefer HaShorashim) and Malbim (Tehillim 3:3, Chavakuk 3:3): selah is an interjection closing an idea, and for Radak a musical direction to lift the voice at the close; Malbim adds that it can mark off a parenthetical remark from the main line. Rabbi Chaim Friedlander: it signals that an important idea has just ended and one should pause and take it in. Rabbi Aviad Sar-Shalom Basilea faulted Radak for seeming to set aside the Gemara's reading; Rabbi Yaakov Emden defended him, that Radak gives the pshat and the tradition gives the deeper sense. Ibn Ezra: selah affirms that what was just said is true, roughly "so it is." Mecklenburg himself ties selah to suleh (Iyov 28:16), which denotes something of higher value, and elsewhere cites one of the earlier commentators who apparently wrote that Selah is one of the Names of Hashem.

va'ed / ad (ועד, עד)

Root ע-ד. Wertheimer: ad literally means "until," and left hanging with no object it is an ellipsis, "until... (a time that cannot be named)," so it denotes infinite duration. Mecklenburg links va'ed to adi'im, "adornments," the eternal ornaments of the soul in the World to Come.

Whether the three words carry "forever" everywhere or only beside olam is disputed: Rabbi Avraham ben Ezriel of Vienna limits the Gemara's ruling to verses where they stand next to olam; Maharsha takes it as a general lexical finding. Rabbi Menachem ibn Saruk (Machaberes Menachem) and Rabbi Yosef Kimchi (Sefer HaGilui) treat them as flat synonyms; Kimchi leaves selah off the list. Rashi's own account of Eruvin 54a is the simple one: they mean the same because they appear together.

Rendering guidance

Le'olam in a din: render by the actual span ("for as long as he lives," "until the Yovel") or write "forever" and gloss it, since Rashi's cap is the standard reading. Never let it stand as bare "forever" where the halachah turns on the limit.
The triple in the berachah said just before Shema in the morning, נצח סלה ועד ("Your mercy and Your kindness shall not forsake us"): English "forever" will swallow all three. Wertheimer's grid gives the way out: "unceasingly, continually, for all eternity." That the words differ is precisely the dispute: Rabbi Avraham ben Natan HaYarchi and Abudraham held the phrase redundant and would say only va'ed; Rabbi Yitzchak Abuhab kept all three, the piling-up being the point.
Selah in Tehillim: leave it as selah. Choosing "forever" (the Gemara) or a pause marker (Radak, Malbim) hides a real machlokes, and no English word holds both.
Trap: "eternal" absorbs olam and netzach alike. Reserve it for netzach and give olam a phrase with time in it ("for all time," "for generations").

Sources

Rabbi Reuven Chaim Klein, "Forever and Ever," What's in a Word?, Ohr Somayach, 25 Shevat 5778 (2018-02-10), https://articles.ohr.edu/articles/forever-and-ever; raw text in sources/whats-in-a-word/raw/7633-forever-and-ever.md. Primary loci: Shemos 21:6 with Rashi; Eruvin 54a; Tehillim 3:3 with Rashi, Meiri, Radak, Malbim and Ibn Ezra; Chavakuk 3:3 (Malbim); Iyov 28:16 (suleh); Radak, Sefer HaShorashim; ibn Saruk, Machaberes Menachem; Rabbi Yosef Kimchi, Sefer HaGilui; Rabbi Aviad Sar-Shalom Basilea, Emunas Chachamim. Nothing the article carries is omitted here, including its Greek (Aquilas) and Syriac (Peshitta) versions alongside Targum Yonasan.