[inigma]

Elven would equate to American
Elvish would equate to Americanish

Drop the "h" and you'll understand what happened to a famous singer.

Elvish would be "elf-like" for "ish" means "like," or "as unto".

Elven is an adjective. It would be used to describe the people, places, and things related to an elf.

Elvish is also an adjective. It would be used to describe nouns that are "like" Elven. To say a sword made by an elf is an Elvish swords is to use improper english. It is more proper to say that that it is an Elven sword.

However, a sword made by a human to look like an Elven sword would in fact be properly called an Elvish sword.

When describing a noun's relationship to an elf, it is Elven.

When describing a elf-like noun's relationship to anything other than an elf, it is Elvish.

Same goes for other creatures.

For example, you say it's an "American car" or "Japanese car." You never say it's an "Americanish car" or a "Japanesish car."