adjectival word-forming element, variant of -al (1) with connective -i-. From Latin -ialis, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective.
suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).
a "connective" element in many words formed with Latin or Greek suffixes, now often felt as part of them (as in -iac, -iacal, -ial, -ian, -ify, -ity, etc.). Properly it forms no proper part of the suffix but is often the stem-vowel of the initial word in the Latin compounds (genial from genius), or a modified form of it. As such forms were very common, -i- was used merely connectively or euphonically in some Latin compounds (uniformis) and in later words made from Latin components in English or French (centennial, editorial).
The Greek equivalent is -o-, which also became an active connective in English, but they now are used indifferently with elements from either language.
