The difference between 丸 and 玉


It may be a dumb question, both mean circle/round thing but 玉 is more of a
jewel/sphere/ball. Could I say "5円丸" instead of "5円玉"? Or should I just stick
with "5円硬貨"




When I was a kid, some older people did actually called coins as:

> 「[Number] 円丸{えんまる}」

Now that those people are gone, I no longer encounter that usage anywhere. It
might have been a regional (Nagoya, in my case) and/or old way of calling
coins. You would look quite weird if you used it today.

In informal daily speech, we almost exclusively use:

> 「[number] 円玉{えんだま}」

Only in very formal situations, we use:

> 「[Number] 円硬貨{えんこうか}」

Most people just do not actively use the last one much even though everyone
knows what it means.

