Fob and Key ring

Fob noun - Short chain or ribbon attaching a pocket watch to a man's vest.

Key ring and fob are semantically related in charm topic. In some cases you can use "Key ring" instead a noun "Fob", when it comes to topics like pendant, keychain, keyring.

Key ring noun - A circular ring of metal for holding keys.

Fob and key ring are semantically related in charm topic. You can use "Fob" instead a noun phrase "Key ring", if it concerns topics such as pendant, keychain, keyring.