circle, yen, round
円 centers on the shape of a circle and things that are round. The yen sense is a specific application of that round shape, as coins are round.
円 is the modern simplified form of 圓. The older form combines 囗 (enclosure) with 員, which likely contributed the sound and the idea of roundness. The modern form is a stylized simplification.
The outer frame 冂 with a horizontal line inside looks like a round coin or a circle with a line through it. Picture a yen coin: round and circular.
For エン, imagine a perfectly round yen coin with the letter 'N' stamped on it: 'N' -> エン, and the coin is a circle.
yen (currency of Japan)
disk; discus; platter
round shape; circle; circular form
smooth; undisturbed; uninterrupted; harmonious
ellipse; oval
harmonious; peaceful; happy; amicable; smooth; free from trouble
circumference
round table
cylinder
column; shaft; cylinder
arc
ripeness; mellowness; maturity
yen basis (for trade, exchange, etc.)
1000 yen
hundred-yen store; dollar store
one yen
depreciation of the yen; weak yen
yen exchange rate
appreciation of the yen; strong yen
1,000 yen bill
elliptical shape; oval shape