Gerousia (γερουσία) means 'council of elders' or 'senate' — the assembled body of senior leaders. It appears only once in the New Testament (Acts 5:21), where it refers to the full council of elders of Israel summoned by the high priest. The word derives from geron (old man/elder).
In Acts 5:21, Luke distinguishes the Sanhedrin from the gerousia: 'they called together the Sanhedrin — the full assembly of elders [gerousia] of Israel.' This suggests the gerousia was either the larger assembly of elders or a formal synonym. In Hellenistic Judaism, the gerousia was the civic body that governed Jewish communities. The theological significance is the institution of elder leadership as the authoritative structure of God's people — from the elders of Moses (Exodus 24:1) to the elders of Israel to the elders of the churches (Titus 1:5). God governs His people through servant leadership of tested elders.