SIT ABOUT – sit somewhere doing nothing and wasting time

In any difficult situation, Florence prefers to sit about hoping somebody else will solve her problems.

SIT BACK – 1) to sit somewhere and relax; 2) to not be involved in something or stop making any efforts

Nicole sat back (1) on the sofa and prepared to watch the "show": she and Toy, her friend from college, just caught Toy's boyfriend cheating on her with another girl. While Toy and her boyfriend were quarreling, that girl just sat back (2) and let them settle the problem themselves as if she wasn’t involved at all.

SIT BY – 1) sit next to someone; 2) to refuse to stop something illegal, bad or just unpleasant from happening

My father told me to sit by (1) him. I already knew that he was going to say something like, “I can’t sit by (2) watching you ruin your life! And blah blah”.

SIT FOR – 1) to pose as a model; 2) to take care of children when their parents are out

Yan Goght invited me to his personal studio to sit for (1) a portrait. Unfortunately, I missed that opportunity because my aunt asked me to sit for (2) her children.

SIT IN – to take part in a non-violent protest where people go somewhere and stay there refusing to move

On March 27, about three hundred college students sat in to protest against tuition fee increment.

SIT IN FOR – to be a substitute for someone

Terry could easily sit in for his boss. He supposed everybody was able to perform the boss's duties - just scream at your subordinates, sign documents and steal money from the company’s budget.

SIT IN ON – to attend something (a meeting, course etc.) as a visitor or guest rather than a regular participant

As Mishel didn’t contribute significantly to the organization, he could just sit in on the meetings and listen to other participants

SIT ON – 1) to suppress or hide something; 2) to postpone dealing with something

It was revealed that Medical M sat on (1) reports showing the presence of toxic components in their medicine but the police keeps sitting on (2) the investigation of this case.

SIT OUT – 1) to refrain from taking part in something; 2) to stay till the end of the event

“I’m exhausted! I better sit this round out (1)!”

“Okay, but please, you have to stay here and sit it out (2). They gonna give us good prizes at the end of the game”

SIT THROUGH – to stay until something is finished

Lory wants to sit this boring movie through to see if the main character would stay alive or not.

SIT UP – 1) to be awake at the time you usually go to bed; 2) to suddenly show interest, excitement or just pay attention to something

I was sitting up (1) late last night drinking and watching TV when a strange sound upstairs made me sit up (2).