-tis

From Proto-Italic *-tis, from Proto-Indo-European *-tis, suffix forming nouns from verbal roots.

• (Classical Latin) IPA^(key): [tɪs]
• (modern Italianate Ecclesiastical) IPA^(key): [tis]

-tis f (genitive -tis); third declension

1. (unproductive) suffix found in certain nouns originally derived from verbs

• This suffix appears as part of some inherited nouns, but is not productively used to derive new nouns in Latin. Its function was taken over by other synonymous suffixes; in particular, the extended form -tiō f. Furthermore, many nouns that originally ended in *-tis lost the vowel *-i- in their nominative singular, making new nominative singular forms that ended in *-ts, which was simplified to Latin -s. For example, Proto-Indo-European *méntis (“thought”) became pre-Latin *ments, yielding historical Latin mēns (“mind”), oblique stem ment(i)- (as in genitive singular mentis, genitive plural mentium): the same root is found in the Latin verb meminī (“to remember, bear in mind”). Other similarly formed nouns include mors (“death”), oblique stem mort(i)-, from the root of morior (“to die”), and fors (“chance”), oblique stem fort(i)-. However, this loss of *-i- was prevented in nouns with certain phonological forms, probably for the sake of avoiding particularly awkward consonant clusters: for example, vestis, restis and messis, tussis.
• As in other cases, suffix-initial -t- was regularly replaced with -s- after a verb root ending in a dental plosive (-t- or -d-), and the resulting cluster was regularly assimilated to -ss-.
• Etymologically, this suffix inflected with i-stem endings, but as with other i-stem nouns, certain case endings were altered by analogy with consonant-stem nouns. Different nouns varied in the extent to which they adopted consonant-stem endings in the oblique cases: for example, tussis almost always uses the i-stem accusative singular tussim, whereas vestis uses the accusative singular vestem, and messis is attested in the accusative singular both as messim and (more often) as messem.
• Based on old i-stem adverbial accusatives such as partim, the ending -tim gained an independent use as a productive suffix forming adverbs.
• Words formed with this suffix are generally feminine, but some masculine exceptions exist, such as fūstis m (“cudgel”), vectis m (“bar; lever, crowbar; bolt”).

Third-declension noun (i-stem).

• (Classical Latin) IPA^(key): [tiːs]
• (modern Italianate Ecclesiastical) IPA^(key): [tis]

-tīs

1. masculine/feminine/neuter dative/ablative plural of -tus

• Vowles, Guy Richard (1928), “Studies in Greek Noun Formation”, in Classical Philology, volume 23, page 35
• Lindsay, W. M. (1894), The Latin Language, pages 340-342