puter.

From a stem *pŭtri-, commonly considered a close cognate to Old Irish othar m (“sickness”) (from a stem pŭtro-), from Proto-Indo-European *puH- (“rotten, foul”) (also the source of Latin pūs (“pus, foul matter”) and pūteō (“to be rotten”) and English foul; see links for additional cognates). It is uncertain why *pŭtri- and *pŭtro- have short *ŭ, since the rules for the evolution of preconsonantal Proto-Indo-European *-uH- in Italic and Celtic are disputed. Proposed explanations include: *shortening of long vowels in a pretonic syllable (*puH-trí- > *pūtrí- > putri-) (sometimes called "Dybo's Law"). As there are a number of apparent counterexamples to this sound change, it is often proposed that it was only regular in certain conditions, but there is no agreement on what those conditions were. *simplification of a laryngeal before a two-consonant *-TC- sequence, or more specifically, before a stop + resonant + vowel (sometimes called the "Weather Rule", "Wetter-Regel" or "WR") *a variant root form *pHu-. (However, Zair 2012 argues that the sequences *CHiC-/*CHuC- probably underwent metathesis to *CiHC-/*CuHC- in Proto-Indo-European.) Like all other Latin three-termination third-declension adjectives, the nominative forms were affected by a combination of sound changes and analogy. The masculine nominative singular puter (rare; found in Varro and Ovid) would be the regular phonetic outcome of an earlier form *putr̥s (with syllabic *r̥), from syncope of original putris. (Compare ter from Proto-Indo-European *trís.) It is also declined as a two-termination adjective with the alternative masculine nominative singular putris (e.g. "lapis ipse gracilis et putris", Pliny Epistulae 10.39).