συγκάθημαιsynkáthēmai

to sit together or with: with dative, Acts 26:30; followed by μετά, with genitive, Mark 14:54.

Greek (New Testament) · G4775

Same root

σύνsýn · G4862with or together (but much closer than G3326 (μετά) or G3844 (παρά)), i.e. by association, companionship, process, resemblance, possession, instrumentality, addition, etc.
κάθημαιkáthēmai · G2521and (to sit; akin to the base of G1476 (ἑδραῖος)); to sit down; figuratively, to remain, reside

Where it appears

Appears 2 times in the Bible.

Mark 14:54 Meanwhile, Peter followed him at a distance and went right into the high priest’s courtyard. There he sat with the guards, warming himself by the fire.
Acts 26:30 Then the king, the governor, Bernice, and all the others stood and left.

Source: G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922), public domain.