What words end in "on" as a singular, and end in "a" as a plural??

Question

What words end in "on" as a singular, and end in "a" as a plural??

Answer 1

There are quite a few, but I'll give some examples!

Well-known ones:

- Phenomenon (singular), phenomena (plural)

A fact or situation that is observed to exist or happen, especially one whose cause is in question.

- Criterion (singular), criteria (plural)

A principle or standard by which something may be judged or decided.

- Automaton (singular), automata (plural)

A moving mechanical device made in imitation of a human.

Uncommon ones:

- Amnion (singular), amnia (plural) ... or amnions (plural)

The innermost membrane that encloses the embryo of a mammal, bird or reptile.

- Anthelion (singular), anthelia (plural)

A luminous halo around a shadow projected by the sun onto a cloud or fog.

- Anthemion (singular), anthemia (plural)

An ornamental design of alternating motifs resembling clusters of narrow leaves or honeysuckle petals.

If you would like some more I'd be happy to add them!

Hope this helps/is of some interest!