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.


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].

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

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