Recently, I discovered the existence of key.
This tag is currently being used for both cryptographic keys (SSH/GPG/RSA/etc.) as well as keys on one's keyboard.
A tag that functions like this has, in my opinion, no reason to exist. The tag is simply too generic and is better handled by other tags.
For the cryptographic example, most questions can be tagged ssh, gpg, etc. For keyboards, valid tags would be (obviously) keyboard, keyboard-shortcuts, etc.
Due to the nature of this tag, it's probably bad to synonymize it and it's bad to keep around. However, I don't think blacklisting is (yet) a viable option. Perhaps just deleting/retagging the existing tag will suffice?