The etymology of seven

Yesterday we took a look at four explanations for the the bizarre nature of the number 'six' in Indo-European languages. The number six probably evolved under phonological influence from seven; though the precise nature of this influence is disputed. Today, let's take a look at a far more palatable word to reconstruct, the number seven. As we did with the number six, let's arrange a table of reflexes.

Anatolian Hittite šiptamii̯a- "liquid from seven ingredients"
Italo-Faliscan Latin septem
HellenicGreek ἑπτά
Balto-SlavicLithuanian septynì ; Old Church Slavonic sedmь
Armenian ewt'n
Celtic Old Irish secht- ; Welsh saith ; Gaulish sextan- "sixth"
Albanian shtatë
Tocharian Tocharian A ṣpät ; Tocharian B ṣukt
Germanic Gothic sibun ; Old Norse sjau ; Old High Germanic sibun
Indo-IranianSanskrit saptá ; Young Avestan hapta- ; Mitanni satta-
Non-IEHurrian šittanna "seven laps" ; Georgian švid ; Svan išgwid

The oldest Indo-European languages are united that the original Proto-Indo-European word was *septm̥. As in the case of 'six,' the Greek /h/ stems from an earlier *s; the ending -a in Indo-Iranian derives from the syllabic *m̥; and Verner's Law in Gothic tells us that the accent in PIE *septm̥ would have been on the second syllable (Beekes 2011).

But since I brought up Gothic, let's take a look at the problem of the Germanic languages. While the *p in *septm̥ is recoverable, none of the Germanic languages point to the existence of a putative *t, even though there is no reason the sound would have disappeared. This incongruity gave Vennemann (1995) the justification he needed to point to a Semitic loan (compare Akkadian sebū/sebettum (if you dig a little deeper you see that Vennemann doesn't mention that those are the ordinal versions of the numbers)) but assuming an irregular loss of *t is parsimonious. 

Latching on to the Semitic connection, however, is Mallory & Adams (1997), who view the Proto-Indo-European *septm̥ as too similar to the feminine Proto-Semitic *s-b-'tu "seven" to ignore. This isn't beyond the boundary of belief. Proto-Kartvelian *šwid- (with reflexes listed in Georgian and Svan above) is believed to stem from Akkadian šibit "seven" (Klimov 1998).

Beekes, Robert. Comparative Indo-European Linguistics. John Benjamins Publishing. 2011.

Klimov, Georgii. Etymological Dictionary of the Kartvelian Languages. Walter de Gruyter. 1998.

Mallory, J. P. & Douglas Adams. Encyclopedia of Indo-European Culture. Taylor & Francis. 1997.

Vennemann, Theo. "Etymologische Beziehungen im Alten Europa" in Der Ginkgo-Baum: Germanistisches Jahrbuch für Nordeuropa. Helsinki. 1995.