Wiktionary
vb. To attend a private meeting without participating.
Usage examples of "sit in on".
After all, there was no practical reason for the squadron's senior medical officer to sit in on a discussion of tactics .
Is there any chance you could sit in on a meeting here say, five or so?
He would have expected the old bastard to want to sit in on the discussion and giggle silently - here's one more intransigent pupil up for the axe.
A year or so into that, I was asked to sit in on a meetingjust to keep notes, fetch coffee, and look presentable as Roarke himself would be attending.
It was intense all right and got steadily more so, but-Jubal, ever sit in on a spiritualist sé.
It was intense all right and got steadily more so, but- Jubal, ever sit in on a spiritualist s’.
While it was not part of their regular curriculum, more and more of them had begun to forgo their own siestas to sit in on the lessons Zaranda gave Shield.