-a 1
a plural ending of nouns borrowed from Greek and Latin: phenomena; criteria; data; errata; genera.
-a 2
a feminine singular ending of nouns borrowed from Latin and Greek, also used in Neo-Latin coinages to Latinize bases of any origin, and as a Latin substitute for the feminine ending - e of Greek words: anabaena; cinchona; pachysandra.
-a 3
an ending of personal names forming feminines from masculines: Georgia; Roberta.
[ -a (see -A 2 ), as Claudia, fem. of Claudius ]
-a 4
a suffix designating the oxide of the chemical element denoted by the stem: alumina; ceria; thoria.
[ prob. generalized from the -a of MAGNESIA ]