Is there a difference between ירחים and חדשים?

Question

As a word meaning "months," the word חדשים is used in Ber. 38:24 and then multiple locations after Sh'mot 12:2.

יְרָחִים appears in Sh'mot 2:2, then (possibly) in Dev 33:14 and twice in Iyov.

When they refer to "months" do they both refer to the same thing or is there a difference (in meaning or reference)? Why would these 3.5 instances choose Yerachim over Chodashim? I thought that maybe a yerach was a moon cycle (from whatever point the moon is at to the next instance of that same point) while a chodesh was based on the newness (so "new to new") but I have no basis for that.

Answer 1

ירח has its name based on the rotation it follows, that the moon's light it renewed from each rotation to the next (מירח לירח). Therefore it says (Tehilim 104:19), He made the moon (ירח) to mark the seasons, saying the God established the time-cycle of the moon to the days of the month (חדש) so that mankind will have a signal to establish its correct time-cycle. Or that a person can say to his friend, in another month I will pay you, or I'll do X for you at X time.

It is written in (מדרש כת"י תימני), a חדש is the beginning of the month, and ירח is the end.

In the Talmud, Sanhedrin 11a, it says a חדש is 29 days. In Yebamot 48b it says ירח is 30 days.

Thus, Chodesh is a direct reference to a set amount of time, which is consistent, whilst Yareach is in correlation with activity of the moon (cf. Aderet Eliyahu on Dev 33:14)

Just as a personal rule I noticed, chodesh means month in the normal English sense of the word, when the word yareach is used, it is telling you something [see above, perhaps].

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Select explanations above taken from ספר באור שמות הנרדפים by ורטהימר, שלמה אהרן בן יעקב, 1866-1935.

Answer 2

Some answer that chodesh is Aramaic, while yerach is Hebrew.

The Malbim and Rabbi Samson Raphael Hirsch (1808-1888) explain that the primary meaning of the word chodesh is not “month” but rather “beginning of the month.” In this way we find that the word chodesh appears in the Bible when one would otherwise expect the phrase Rosh Chodesh to appear (see Num. 28:14, I Sam 20:18, and Isa. 1:13). The word chodesh, therefore, primarily refers to the concept of chadash (“new”) or chiddush (“novel” or “renewal”), and specifically denotes the novelty of the month. That chodesh also refers to the idea of a “month” is only a secondary, borrowed meaning. If Chodesh denotes the beginning of the month, then maybe yerach denotes the entire month as a whole.

The Malbim explains that the word yerach simply denotes a period of thirty days — regardless of whether or not those thirty days represent an astronomical event related to the moon.

Rabbi Aharon Marcus (1843-1916) writes that the word yerach is related to the Hebrew word oraiach (“path”) and to the Aramaic word אתרחיש(“it happened”). He does not explain the thematic link between these words.

Rabbi Hirsch argues that the word chodesh denotes the idea of a month as simply a unit of time (measured by the amount of time it takes the moon’s light to disappear and reappear). In this way, the word chodesh is transcendental, or abstract. On the other hand, he explains, the word yerach connotes the month as a vehicle for maturation.

Interestingly, Rabbi Mordechai Jaffe (1530-1612), the author of the Levush, writes that the custom is to refer to the month on a divorce document (a get) as a yerach, and on a marriage document (a ketubah) as a chodesh.

SOURCE: What's in a Word?, "Old Month versus New Month", see also this page from the Veromemanu Foundation for Biblical Etymology