[Latin or Greek noun endings.]
Some nouns in this ending have been adopted unchanged from classical Latin or Greek: fascia, mania, militia, onomatopoeia (the formation of a word from a sound associated with what is named). Some terms created in recent centuries but based on Latin or Greek also contain it: encyclopedia, utopia.
A second set comprises names of medical states and disorders whose names are derived from Latin or Greek roots: anorexia, catatonia, chlamydia, diphtheria, dyslexia, hysteria, paraplegia, pneumonia.
The ending occurs in many name for living things, which are often derived from proper names. Most are of plants: dahlia, gardenia, lobelia, magnolia, poinsettia, wisteria. A few are of other organisms: latimeria (a genus of coelacanth), leishmania (a genus of a single-celled parasitic protozoan). See also -a2.
A number of country and other place names have names ending in -ia: Bohemia, Cambodia, India, Nigeria, Russia, Sardinia, Virginia. It also marks the names of some oxides of metallic elements whose names end in -ium: lithia, magnesia, thoria, zirconia.