rain out = cancel because of rain or bad weather

Our canoe trip got rained out so we rescheduled it. (almost always used in the passive voice)

right away = immediately; now

If he doesn’t get help right away, he’ll drown in the quicksand.

right on = an exclamation of happiness or approval; also means that something is correct or accurate.

"Oh yeah! Right on! I just found out that the stock investment I made yesterday doubled already!"

run across = to find information; to meet someone or something suddenly.

Whenever my grandmother runs across an interesting passage in the Bible, she emails it to me.

run down = to review a list of things or read something quickly.

Let’s run down this list of candidates for the new sales position.

rundown = (adjective) a feeling of fatigue; tired.

Patricia has been feeling kind of rundown lately. It’s probably because she’s pregnant.