What is the synonym of key?

The synonym of "key" depends on the context. Here are a few possibilities:

For a physical key:

* Lock: (used as a noun)

* Unlocker: (used as a noun)

* Passage: (used as a noun, referring to a way to access something)

* Access: (used as a noun or verb, referring to the ability to get to something)

For a key in a figurative sense:

* Solution: (used as a noun, referring to an answer to a problem)

* Answer: (used as a noun, referring to the solution to a question)

* Clue: (used as a noun, referring to a piece of information that helps to solve a mystery)

* Essential: (used as an adjective, referring to something that is crucial)

* Important: (used as an adjective, referring to something that is significant)

* Fundamental: (used as an adjective, referring to something that is basic or essential)

For a key on a keyboard:

* Button: (used as a noun, referring to a button that can be pressed)

Please provide more context so I can give you a more specific synonym for "key"!