sit tight

hang tight

To wait, without attempting to address a challenging, alarming, or dangerous situation, until a later point in time.

sit back

To relax, to not exert oneself.

sit in

To attend a class, educational presentation, meeting, etc. for one time, as a visitor.

sit in for

To substitute; to take somebody's place.

sit in with

To join (often as an observer, supervisor or outsider) a group working together on a task.

sit on

To block, suppress, restrain (something).

sit on a tack

An expression of contempt or dismissiveness directed at someone, particularly in the case of disagreement.

sit on one's ass

To be very lazy and idle, especially when immediate action is required.