key

noun:a small piece of shaped metal used to operate a lock
- I couldn't get into the house because I had lost my key.
adjective:of great importance or significance
- Education is the key to breaking the cycle of poverty.
- The key factor in their success was customer service.
- Communication is key to a successful relationship.
noun:a button on a keyboard that produces a particular character or function
- Press the Enter key to submit your response.