Directed or moving upwards.
- Synonyms: high, raised, lifted and elevated
The flag is up.
Toward the top or away from the Earth.
- Synonyms: upward, higher and above
- Antonyms: down, downward and lower
The balloon went up.
If a task or result is up to you, it means you are in charge of deciding or doing it.
The outcome of the game is up to the players.

It is up to you to choose the restaurant for dinner .
If you are up to something, you are doing or planning it.
What are you up to this evening?

We had better make sure he's not up to something stupid again.

She's always up to some kind of trouble.
Positive.
- Synonyms: positive, good and pleasant
It was an up day.
(not before a noun) Cheerful, optimistic.
- Synonyms: cheerful, optimistic, positive and lighthearted
He is feeling up.
(not before a noun) Happening, occurring.
- Synonyms: happening, occurring, passing, in transition and new
What’s up?

They act like something is up.
(not before a noun) Wrong.
- Synonyms: wrong, problematic and troubling
Something is up with him.
(not before a noun) Finished.
- Synonyms: finished, over, done and discovered
It is all up with them.

Preposition

Noun