Trinoda Necessitas
Black's Law Dictionary · Henry Campbell Black, M.A. · 1910
Black's Law Dictionary
Lat. In Saxon law. A threefold necessity or burden. A term used to denote the three things from contributing to the performance of which no lands were exempted, viz., pontis reparatio, (the repair of bridges,) arcis constructio, (the building of castles,) et expeditio contra hostem, (military service against an enemy.) 1 Bl. Comm. 263, 357.