An etrog (אֶתְרוֹג, also pronounced "esrog") is a yellow (or lime-colored) citrus fruit used by Jews during the week-long holiday of Sukkot as one of the Four Species. It is also known as a citron or a citrus medica. Every day of Sukkot, except for Shabbat, the etrog is taken in hand together with a bundle containing a lulav (palm frond), three hadasim (myrtles) and two aravot (willows) waved in each direction.

Read: What Are the Four Kinds?

The Identity of the Etrog

There are several varieties of etrog used by Jews today, each of which has been carefully identified by successive generations of Jews. There are etrogim from Yemen, the types grown in Israel, and the variety from the Calabria region of Italy, which are favored by many. The Calabrian variety is unique in that by the time it matures, it often does not have the distinctive pitom on its snout.

Read: Why Do People Favor the Italian Etrog?

The Hadar Fruit

The Torah1 describes the fruit which we must take as פרי עץ הדר—pri etz hadar, which translates loosely as the “fruit of a tree which is hadar.” What is hadar?

Since the days of Moses, we have known this to be an etrog. There was never a time when the identity of the fruit needed was in doubt. Rather, each generation told the next generation which fruit was needed to complete the Four Kinds.2 Nevertheless, various propositions were made to demonstrate that this can also be understood from the text.

The common meaning of הדר hadar is “beautiful.” Ibn Ezra3 writes that the etrog is known as the most beautiful of all fruits, and when the Torah tells us to take a beautiful fruit, the only possible candidate is the etrog.

Alternatively, Nachmanides4 writes that hadar is actually the ancient Hebrew name for the etrog, the latter being its Aramaic name. Hence the verse is simply telling us to take the fruit of the etrog tree.

The Etrog in the Talmud

The sages of the Talmud,5 knowing that this term referred to the etrog, found a number of creative ways of seeing the etrog’s distinct properties in the above-mentioned verse:

  1. Focusing on the first two words of the description, “fruit of a tree,” the Talmud understands this to refer to a tree that tastes similar to to its fruit. The wood of the etrog tree is similar in taste to its fruit.
  2. Rabbi Judah the Prince points out that the word הדר hadar can also be rendered as הדיר hadir—a sheep pen. Just as a pen has both old and young animals, so does the tree in question have old and young fruit at the same time. This refers to the etrog tree, whose fruit continues to grow through all seasons, allowing for a single etrog tree to simultaneously hold fruits in multiple stages of growth.
  3. Rabbi Abahu suggests that hadar can also mean “the resident.” This means that this is the fruit which is a resident on its tree—referring to the etrog’s prodigally long growth period.
  4. Ben Azzai said that hadar is etymologically related to the Greek hydor (water)—from which the English word “hydration” is derived. This is a reference to the fact that the etrog tree needs a lot more water than other trees.

As I wrote, all of these suggestions are purely academic, since we have known since the Giving of the Torah that the fruit which we needed to take is the etrog.