In this letter, they write (my translation):
The question was put to a committee headed by Tur-Sinai. In response, they wrote a dictionary of family terms, which can be found on this site (unfortunately, I can't link directly to it - to access it, click on the link הצגת מלון on the right, and then in the drop down menu choose משפחה).
In the listings in the memorial books of the KKL, it is customary to note the relationship between the dedicators and the dedicatees, as in: So-and-so is recorded by his parents, brother, etc ... It is not clear to us if the word nin נין means the son of the grandson or granddaughter, which is the popular usage, but is opposed to the opinion of the commentators.
Also, as to the new words dodan דודן and achyan אחין - it is questionable whether to accept them, and if we do, what is their feminine form.
Most of the terms in the dictionary just have a simple translation - English to Hebrew / Hebrew to English. But a few of them have notes - with the longest one being for their translation of "nephew". They translate nephew as nechdan נכדן (and niece as nechadnit נכדנית) and write:
The committee suggests the word nechdan נכדן (not achyan אחין), on the basis of the fact that in our Medieval literature the word neched נכד had that meaning (nephew), and it is still used in the linguistic traditions of some ethnic groups. It is also worth pointing out that the Latin word nepos, from which are derived the words "nephew" and Neffe (German), is used for both meanings: the son of the son (or son of the daughter) and the son of the brother (or son of the sister). By adding a nun at the end (of neched), as was done with dodan דודן (cousin) from dod דוד (uncle), we achieve the necessary distinction needed today.We'll discuss dod and dodan at a later time, but first a couple of points about their note. The word neched appears three times in the Tanach (Bereshit 21:23, Yishayahu 14:22, Iyov 18:19) - each time paired together in a phrase together with nin נין. We've already noted that while in Modern Hebrew nin means "great-grandson", in Biblical Hebrew it appears to mean "son". According to most commentators, neched in Biblical Hebrew does mean grandson. It doesn't appear much in Talmudic Hebrew (Jastrow offers first "offspring", second "grandson" - and only brings one example.) But the Medieval use of neched as nephew that Tur-Sinai mentions can be found in the Rashbam on Bava Batra 108a.
And to elaborate on the various meanings of the English word "nephew", here's the Online Etymology Dictionary entry:
c.1297, from O.Fr. neveu (O.N.Fr. nevu) "grandson, descendant," from L. nepotem (nom. nepos) "sister's son, grandson, descendant," in post-Augustan L., "nephew," from PIE *nepot- "grandchild," and in a general sense, "male descendant other than son" (cf. Skt. napat "grandson, descendant," O.Pers. napat- "grandson," O.Lith. nepuotis "grandson," O.E. nefa, Ger. Neffe "nephew," O.Ir. nia, gen. niath "son of a sister")."Niece" derives from nephew:
1297, from O.Fr. nièce (12c.), earlier niepce, from L. neptia, from neptis "granddaughter," in L.L. "niece," fem. of nepos "grandson, nephew". Replaced O.E. nift, from P.Gmc. *neftiz, from the same PIE root. Until c.1600, it also could mean "a granddaughter" or any remote female descendant.And the word nepotism is also connected:
According to Almagor-Ramon (Rega Shel Ivrit #19), the double meaning of the Latin term nepos influenced the Hebrew usage of neched in the Middle Ages.
"favoritism shown to relatives, esp. in appointment to high office," 1662, from Fr. népotisme, from It. nepotismo, from nepote "nephew," from L. nepotem (nom. nepos) "grandson, nephew". Originally, privileges granted to a pope's "nephew" which was a euphemism for his natural son.
However, the official suggestion of nechdan ran into trouble early on. In 1948 Avinery wrote (published in Yad Halashon, page 389) that we shouldn't be surprised that there was no word for nephew in Hebrew. Ancient people weren't as careful about family titles as we are today, and even terms like av אב, ach אח and dod דוד didn't always mean father, brother and uncle (respectively).
He continues to say that he agrees with the committee's rejection of achyan for nephew, but nechdan has not caught on either - either in speech or in literature. His suggestion? To use the word nin for nephew. On the one hand, he prefers the Biblical shilesh שילש - "one of the third generation" - for great-grandson. On the other hand, he brings a few examples from the 1930s where nin or nina נינה was used for nephew or niece. For example, in 1931, HaAretz referred to Lord Balfour's niece, Blanche Dugdale, as his nina.
But this suggestion also didn't stick. The common term used today for nephew is achyan, and achyanit אחיינית is used for niece. It's not clear to me when (or why) achyan gained its popularity. I asked a neighbor of mine, who's in his sixties, if he grew up using the word achyan. He said no, when he was growing up, he'd say ben-ach בן-אח, and that achyan has only been used in the past 30 years or so.
Despite its new usage as nephew, the word itself goes back to Biblical times - it was the name of a member of the tribe of Menashe, listed in Divrei HaYamim I 7:19. As with most Biblical names, there is no clear etymology. Some sources suggest it meant "brotherly or fraternal"; others (Who's Who in the Jewish Bible by David Mandel) offer "younger brother". Yehuda Kil in Daat Mikra mentions that "some say" that it means nephew. I'm very curious who suggested that theory, and whether they were influenced by the modern meaning of the word...