key

noun1 of 2

something you use to open a lock or start a car

• “I want to make you think about a key point.”Tatoeba
• “You should always have spare keys in a safe place.”Tatoeba

Sentences from Tatoeba show real usage. A word can have several meanings, so a sentence may use another one.

verb2 of 2

To mark or indicate with a symbol indicating membership in a class.