sit in

To attend a lesson or meeting as a visitor, usually to watch and listen.

• You're welcome to sit in today.
• She sat in on the meeting to learn about the project.
• Could we sit in on one of your lessons?

How to use it: sit in on something (Can I sit in on your history class?)

Similar words: observe, attend as a guest

Common phrases: sit in on something, sit in quietly, sit in today

To stay seated in a place as a protest, often refusing to leave.

• The students sat in all night.
• Workers are sitting in at the factory until talks begin.
• They sat in outside the office to demand equal rights.

How to use it: sit in at a place (Students sat in at the college to protest the new fees.)

Similar words: stage a sit-in, occupy

Common phrases: sit in peacefully, sit in all night, sit in outside

To join a band or group for a performance as a guest musician.

• Can I sit in tonight?
• He sat in with a jazz band last Friday.
• Their usual drummer was pleased to let her sit in.

How to use it: sit in with a band (A local guitarist sat in with the band.); sit in on an instrument (She sat in on piano for the final song.)

Similar words: guest, play as a guest

Common phrases: sit in with someone, sit in on drums, sit in tonight