Translation guide
A small chain or ring for holding keys. In Japanese, the most common term is キーホルダー, but other words exist depending on the type.
keychain (general)
The most common way to refer to a keychain, often with a charm or decoration.
The standard loanword for 'keychain' or 'key holder'. Used for both functional and decorative keychains.
This keychain is a souvenir from a friend.
I bought a new keychain.
Refers specifically to a key ring, the metal loop that holds keys. Less common for decorative items.
Put the key on the key ring.
A less common loanword, sometimes used for a chain-style keychain. キーホルダー is more natural.
That keychain has a long chain attached.
A plain metal ring for holding keys, without decoration.
A device or object for holding keys, often mounted on a wall.
For most situations, キーホルダー is the safest and most natural choice. It covers both decorative and functional keychains.
I found a cute keychain.
Attach the key to the key ring.