The numerals and derived numbers of the Proto-Indo-European language (PIE) have been reconstructed by modern linguists based on similarities found across all Indo-European languages.
The following article lists and discusses their hypothesized forms.
Lehmann[6] believes that the numbers greater than ten were constructed separately in the dialect groups and that *ḱm̥tóm originally meant "a large number" rather than specifically "one hundred."
Past sam "even, fine" OIr ceth(a)ir (fem.
pedair) "four" OIr cóic, W pum(p) "five" Gaul suexos "sixth"; OIr sé, W chwe(ch) "six" OIr ocht n- "eight";[h] W wyth "eight" Celtib tekam- "ten";[17] OIr deich, W deg, deng "ten" The numbers three and four had feminine forms with the suffix *-s(o)r-, reconstructed as *t(r)i-sr- and *kʷetwr̥-sr-, respectively.
[5] Special forms of the numerals were used as prefixes, usually to form bahuvrihis (like five-fingered in English): The ordinal numbers are difficult to reconstruct due to their significant variation in the daughter languages.
The following reconstructions are tentative:[20] The cardinals ending in a syllabic nasal (seven, nine, ten) inserted a second nasal before the thematic vowel, resulting in the suffixes *-mó- and *-nó-.
These and the suffix *-t(ó)- spread to neighbouring ordinals, seen for example in Vedic aṣṭamá- "eighth" and Lithuanian deviñtas "ninth".
Reflexes, or descendants of the PIE reconstructed forms in its daughter languages, include the following.