Episunagoge means the act of gathering together — a more intensive compound of sunagoge (synagogue/gathering). The epi- prefix suggests a complete or final gathering. It appears only twice in the NT: Hebrews 10:25 (the gathering of believers in worship) and 2 Thessalonians 2:1 (the eschatological gathering to Christ at His return).
Both uses of episunagoge carry enormous theological weight. Hebrews 10:25 — 'not forsaking the assembling [episunagoge] of ourselves together, as is the manner of some' — grounds corporate worship in eschatological urgency: as the Day approaches, gathering together matters more, not less. 2 Thessalonians 2:1 links our current gathering in worship to the ultimate gathering at Christ's parousia — the final episunagoge when all God's people are gathered to Him. Every Sunday gathering is a foretaste of the great eschatological assembly.