-ia

1.
a noun suffix having restricted application in various fields, as in names of diseases (malaria; anemia), place names (Italia; Romania), names of Roman feasts (Lupercalia), Latin or Latinizing plurals (Amphibia; insignia; Reptilia), and in other loanwords from Latin (militia).
Origin
< Neo-Latin, Latin, Greek, equivalent to -i- (formative or connective) or -ī- (Greek -ei-) + -a, feminine singular or neuter plural noun or adj. ending
British Dictionary definitions for -ia

-ia

suffix
1.
occurring in place names: Albania, Columbia
2.
occurring in names of diseases and pathological disorders: pneumonia, aphasia
3.
occurring in words denoting condition or quality: utopia
4.
occurring in names of botanical genera: acacia, poinsettia
5.
occurring in names of zoological classes: Reptilia
6.
occurring in collective nouns borrowed from Latin: marginalia, memorabilia, regalia
Word Origin
(for senses 1–4) New Latin, from Latin and Greek, suffix of feminine nouns; (for senses 5–6) from Latin, neuter plural suffix
Word Origin and History for -ia

word-forming element in names of countries, diseases, flowers, from Latin and Greek -ia, which forms abstract nouns of feminine gender. In paraphernalia, Mammalia, etc. it represents the Latin and Greek plural suffix of nouns in -ium or -ion.

Chinese forms country names by adding guo "country" to the stressed syllable of the place name, hence Meiguo "America," from mei, the stressed syllable of America (minus -r-, which does not exist in Chinese). Similarly Yingguo "England," Faguo "France." Continent names are similarly formed, with zhou "continent" (e.g. Meizhou "America (continent)," Feizhou "Africa," Ouzhou "Europe").

-ia in Medicine

-ia 1
suff.
Disease; pathological or abnormal condition: anoxia.