[inigma]

It's also phonetically related to Latin:

"en" means "in"

So American (pronounced Ahmehreghkin) means an adjective describing something being related "in" America.

"Ish" does mean "like" as in "it's saucer-like in appearance". Ish implies a disassociation with the connected noun. So Elvish would be anything like an Elf but disassociated with an Elf.

Also, phoneticaly "Elven" is "Elfen" and you start to understand from a phonetical perspective that it's literally "Elf in".

Elf in
Elf like

This is the basic difference between "en" and "ish".