The online etymology dictionary says that arithmetic comes from Greek arithmos, from PIE *re(i)- "to reason, count" and gives as cognates English "read", Old High German "rim" "number", Old Irish rim "number," and Latin ritus "religious custom".

This etymology is suspicious. First, there were no roots starting wit r- in PIE. But this can be explained adding a laryngeal before it. What is more suspicious is that Latin ritus is known to come from the PIE root a̯er- "fit" and cognate to the words artist, army, aristocracy, Aryan, etc.

Also the same dictionary claims that English word row comes from PIE *rei- "to scratch, tear, cut". As to me, the meanings "to tear" and "to reason, count" seem totally different.

Regarding rhythm the dictionary says to come via Greek rhythmos from PIE *sreu- "to flow".

That said, I would like a clarification

  1. Whether Greek rhythmos "arrangement, order, proportion" and arithmos "number" related.

  2. Whether arithmos is related to artist, aristocracy etc.

  3. Where to put English row and Russian ряд "r'ad" meaning "row" (Mallory and Adams put Lithuanian rinda "row" and Latvian rida "in rows" as related to arithmos and count the both related to ratio, artist etc).

  4. Where to put the Italic *ord- "to arrange, arrangement" (> Eng. order), whether it is related to PIE a̯rtus "order, arrangement, juncture" (the dictionary claims it is of unknown origin)

  • 1
    "To scratch" and "to count" are actually not so distant in meaning -- making scratches on a stick or the like is a basic way of keeping count.
    – TKR
    Commented Aug 20, 2014 at 2:12
  • Too many things here. You can't just ask about every word with a rhotic in them. I'd recommend limiting it to just asking about arithmetic, rhythm and their cognates, but not row, ord- etc. Or perhaps ask if *rei- is a PIE homophone.
    – curiousdannii
    Commented Aug 20, 2014 at 7:35
  • I'm voting to close this question as off-topic because it's a language-specific etymology question. Commented Mar 11, 2015 at 3:02
  • @James Grossmann to what language it is specific? The both words exist in English and Russian for instance
    – Anixx
    Commented Mar 11, 2015 at 10:04

1 Answer 1


ἀριθμός and ῥυθμός both have the suffix -θμο-, otherwise they are not related. The mainstream view, as reflected now in Beekes’s Greek etymological dictionary, is that ἀριθμός is from IE *h2rei- ‘to count’, whence also ON rim ‘account’, OHG rīm ‘row, number’, OIr. rim ‘number’, and ‘probably’, Lat. rītus ‘religious observance, rite’ < *h2rei-ti-.

ῥυθμός is from *sreu- “to stream”.

The origin of ἄριστος “best” (as in aristocracy etc.) is considered to be uncertain, but it cannot very well be connected to the aforementioned words, nor with Latin ars (as in artist).

  • Are you sure with the last paragraph? We have in PIE a̯ermntom fit a̯ermos fitting a̯eri̯os peer, freeman, honest a̯rtos fitted a̯ristos of the best sort a̯rtis correct, exact a̯rtus order, arrangement
    – Anixx
    Commented Aug 19, 2014 at 11:54
  • Chantraine does entertain the possibility that aristos is related to the ar- root of ararisko etc., and hence to Latin ars. I don't see any formal reason that shouldn't work.
    – TKR
    Commented Aug 20, 2014 at 17:01

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