Latin Plurals (Data, Media, Etc.)

A number of words derived from Latin that end in –a cause confusion for English speakers. Originally, such words were all plural forms, and their contemporary English usage as singular words is essentially a corruption of their original usage. However, in some cases this usage is so common and widespread that it has become accepted:

• Agenda, though technically a plural word, is completely accepted as a singular count noun whose plural form is agendas.
• Data (the plural form of datum) is also becoming accepted as a singular mass noun, as is media (the plural form of medium) when it refers to things like television, radio, and publications.
• However, some of these words must be treated as plural words in Standard English:

according to this criteria
according to these criteria
according to this criterion

many strange phenomenas
many strange phenomena
an interesting phenomenon