Certain
Part of speech: determiner
Definition: Having been determined but unspecified. The quality of some particular subject or object which is known by the speaker to have been specifically singled out among similar entities of its class.
Part of speech: adjective
Definition: Sure, positive, not doubting.
Example sentence: Everything we do is for the purpose of altering consciousness. We form friendships so that we can feel certain emotions, like love, and avoid others, like loneliness. We eat specific foods to enjoy their fleeting presence on our tongues. We read for the pleasure of thinking another person's thoughts.
Sealed
Part of speech: verb
Definition: To hunt seals.
Part of speech: adjective
Definition: Closed by a seal.Preventing entrance.Not subclassable; from which one cannot inherit.
Example sentence: People - especially the geeks who created it - have tended to look at the Internet as something that's hermetically sealed: there's the Internet and the rest of the world. But that's not how people want to use the Internet. They want to use it as a way of better navigating the real world.