5.4.1. In Europaio, as in English, there are three degrees of comparison: the Positive, the Comparative and the Superlative.
NOTE. There were degrees neither in IE II nor in the Anatolian dialects. It is, therefore, an innovation of IE III, further developed by each dialect after the great migrations.
5.4.2. The Comparative is generally formed by adding -ios, which also has the variants -ijos and -ison; as in senioses, kak-ios-es, mew-ios-es, meg-ios-a, etc.
5.4.3. The same suffix is the base for the Superlative -isto (from -is-to); as in begtistos, newistos,...
Other Superlative suffixes, not general, include: oi. and gr. -tero, gr. -tatos, oi. -tamo, ita. and cel. -amo, -samo, -tamo, and extended -is-samo -upermo, lat. summus < sup-mos; ádhamas, lat. infimus < ndh-mos; lat. maximus < mag-s-mos; lat. intimus (cf. intus)< en-/n-t-mos. These are all derivatives of the suffix -mo (i.e., -mo or -[']mo). The suffix is also present in other adjectives, but here it has taken the Superlative degree.
5.4.4. It is interesting to point out that both suffixes, -ios (and -tero) and -isto, had probably an original nominal meaning. Thus, the elongations in -ios had a meaning; as in Latin, where junioses and senioses were used for groups of age; or those in -teros, like in matertera, aunt on the mother's side, ekwateros, mule.
NOTE. In Latin (and Germanic), as already said, the intervocalic -s- becomes voiced, and then it is pronounced as the trilled consonant, what is known with the name of rhotacism. Hence lat. iuniores and seniores.