AMERICAN IDIOMS STARTING WITH I
If worst comes to worst:
If things get really bad. ex. "If worst comes to worst, we can always fire him."
Ill-at-ease:
Uncomfortable. ex. "She seemed to be ill-at-ease talking to the doctor about her problems".
In bad taste:
Rude. Vulgar. Obscene. ex. "John's jokes are always in bad taste."
In broad daylight:
Publicly visible in the daytime. ex. "This city is very dangerous. You can get robbed in broad daylight."
In good shape/ condition:
Physically and functionally sound and sturdy. "Shape" is generally used more for people. ex. "The car is in good condition. Bill is in good shape."
In mint condition:
In perfect condition (not used for people).
In no mood to do something:
To not feel like doing something. To not want to do something. ex. "I'm in no mood to cook dinner tonight."
In season:
Currently available for selling (often said of fresh fruit and vegetables). ex. "Tomatoes are very cheap now because they're in season."
In stock:
Available for purchase, as in goods in a store. ex. "Do you have any more of these books in stock? No, I'm sorry we don't."
In the air:
Everywhere. All around.
In the long run:
Over a long period of time. Ultimately. ex. "He smokes a lot now, and I'm afraid that in the long run it will cost him his health."
In the same boat:
In the same situation (usually negative).
In and out:
Coming in and going out often. ex. "She's been in and out all day."
In with:
Friendly with. Friends with. ex. "At high school he was in with the wrong crowd. That's why he always got in trouble."
In advance:
Ahead of time.