*-þiz

From Proto-Indo-European *-ti-s, a widespread feminine action-noun suffix. The suffix belongs to the same Indo-European dental abstract/action-noun system as *-tu-s verbal nouns and *-tó-s verbal adjectives (Fulk 2018: 252–53; Ringe 2017: 74). The surface form of the suffix varied according to accent and the final consonant of the root, though these originally featured zero-grade of the root and suffix accent (Krahe & Meid 1969: 151–52). The suffix assumed different forms based on the final consonants of the base: after -f, -s, and -h, the t- remained unshifted; it was also subject to Verner's Law if the original accent was on the suffix, in which case the t- became a d- (Lehmann 1986a: §4.2.1). Cognates include Sanskrit -ति (-ti), Ancient Greek -τις (-tis), Lithuanian -ti, -tis, Proto-Celtic *-tis, and Proto-Slavic *-tь, all forming nouns of various types.