Forms nouns: disease, abnormal condition, abnormal presence of; -iasis attaches to a root word — typically a pathogen name, a substance, or a body structure — to form a noun naming a disease, infestation, or abnormal pathological condition. It is closely related to -osis (another “condition of” suffix), but with an important distinction: -iasis tends to be used for chronic or recurrent conditions, especially those caused by external agents such as parasites, stones, or infestations, while -osis is broader and can refer to both intrinsic physiological processes and pathological states. In parasitology, -iasis is the preferred suffix for naming infestations/infections caused by a specific organism (e.g., Fasciola + -iasis = fascioliasis). In urology and gastroenterology, it names stone-formation conditions (e.g., nephrolithiasis, cholelithiasis). In dermatology, it names chronic skin conditions (e.g., psoriasis, ichthyosis).
greek - From New Latin-iasis, derived from Greek -asis — an abstract noun suffix expressing “action” or “morbid condition,” from the aorist stems of Greek verbs ending in -aein.
The -i- is a connective vowel joining the root to -asis.
Some sources trace an additional link to Greek ἴασις (íasis), meaning “a healing, cure” — from iatros (“healer”) — though in practice the suffix evolved to mean the disease requiring healing rather than the healing itself.
Entered medical Latin as a standard disease-naming suffix, attested in English from the 17th century onward.
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