Transom: See Mullion.
Transverse: at right angles to the main axis. Specifically applied to the arches and ribs of the vaulting of a nave or aisle that are in the directions of north and south. Compare Longitudinal and Diagonal.
Travertine: a hard limestone found in Tivoli.
Trefoil: See Foil.
Triclinium: dining room of a Roman house.
Triforium: the arcaded passage above the arches of the nave of a Gothic cathedral, opening into the space between the vaulting and roof of the aisle.
Truncated: finishing abruptly instead of in a point. See Pyramid.
Tufa: a volcanic substance of which the hills of Rome are largely composed.
Tumulus: a prehistoric artificial mound, serving as a sepulchral monument.
Tympanum: See Pediment.