[From a Latin plural suffix, or representing the Greek plural ending -ai.]
The -ae suffix is used for the plural of many non-naturalized, specialist, or unfamiliar nouns ending in -a (see -a1) derived from Latin or Greek: antennae is the plural of antenna; larvae of larva; scapulae of scapula, a shoulder-blade; pupae of pupa, a chrysalis. It is increasingly common for such words to have plurals in -as instead. See also -acea, -aceous, -idae, and -inae.
[Derived from a Greek, Latin, or Romance feminine singular ending.]
Many feminine nouns in Greek and Latin had this ending, and a number have been brought over into English unchanged: area, arena, camera, formula, idea, lamina, peninsula. Examples from modern Romance languages include diva, marina, pasta, rumba, and siesta.
Many names for animals or plants derived from or modelled on Latin have this ending: alga, amoeba, cicada, dahlia, fuchsia, hyena, lobelia. It is the usual ending for the oxides of metals, as in alumina, magnesia, and soda.
It forms the ending for many female forenames derived from Latin or Latinized forms, such as Anna, Diana, Julia, Maria, and Victoria. Other female forenames have been created from their male equivalents using -a, as in Alexandra, Georgia, Joanna, Nigella, and Roberta.
A number of geographical terms contain this ending, again taken from Latin precursors, such as Africa, Asia, Corsica, and Malta.
However, many English words ending in -a come from other sources in which the -a does not indicate this suffix: vodka is from Russian, sofa from Arabic, pyjama from Urdu and Persian, satsuma from a Japanese placename, tea via Malay from Chinese, and so on.