Wurdahuzdą: Proto-Germanic dictionary

suffix noun neuter a-stem forms neuter abstract/collective nouns from nouns, often with the collective/comitative prefix *ga- From Proto-Indo-European *-yó-m, the neuter form of the widespread relational/adjectival suffix *-yó-s ‘belonging to, connected with’. The same suffixal complex underlies Proto-Germanic adjectival formations such as *-(i)jaz. The formation was especially productive in combination with the collective prefix *ga-, whose Germanic use as a collective/intensive prefix continues the older sense ‘together, with’ Watkins 2011: 2047. Compare Proto-Slavic *-ьje, a close formal and semantic match, and more broadly Latin -ium and Ancient Greek -ιον, which continue the same Indo-European *-yó-m type as neuter noun-forming suffixes, though not always with a collective function. Meier-Brügger2003: 281–85 describes *-yo-/*-yó- as the most widespread Indo-European suffix for adjectives of belonging or relation. Declension

The suffix varies as *-ją/*-iją based on Siever’s Law: the basic *-ją form is used after a “light” syllable (a short vowel followed by a single consonant), and otherwise, the form becomes *-iją.