複 complicated or compound

The dorky ducky was wearing very complicated FUKU (服).

All corsets on its wings, all garters on its webbed feet.

complicated ★★★☆☆
複 (complicated or compound) + 雑 (miscellaneous , random) = 複雑 (complicated)

complicated; having multiple things that make it complex.

plural ★★☆☆☆
複数 (multiple) + 形 (form) = 複数形 (plural)

Plural - in English ! . . .The Japanese language doesn't really have a word for 'plural,' but Japanese use 複数形 to describe English plurals. So you'll need this word to correct your Japanese friends' frequent grammar boners.
"Look at the deers!"
"Deer doesn't have 複数形、, Yoshio。 3 deer is still 'deer'."
"チクショウ！”

multiple ☆☆☆☆☆
複 (complicated or compound) + 数 (integer, to count) = 複数 (multiple)

multiple (causes of the disease / reasons for the decision / effects of the medicine)