(To) Sit tight
To sit tight is a strange English idiom and it literally means that you sit down squeezing your body in a tight way, which if you did it would be very uncomfortable, not to mention you’ll look really strange.
But if a person tells you to sit tight they want you to wait patiently and take no action until you hear otherwise.
“Mrs. Carter, do you have any idea when the exam results are going to come out?”
“Who knows Johnny, sometimes they come out quickly but it could take some time. You’re just going to have to sit tight and wait.”
8. (To) Pitch in
This English idiom actually makes no sense if you try to take it literally. However, figuratively speaking it means to contribute (give) to something or someone or to join in.
So if your dad tells the family that he wants everyone to pitch in this weekend and help clear the backyard, it means he wants everyone to join in on the efforts to clear the yard and get things done quicker.
“What are you going to buy Sally for her birthday?”
“I don’t know I don’t have much money.”
“Maybe we can all pitch in and buy her something great.”
The above conversation suggests that every one of Sally’s friends should contribute a little bit of money so they can afford to buy her a bigger and better present together.