-st adjective
Etymology: French surbaissé depressed, flattened, surbased (from past participle of surbaisser to lower from above, depress, flatten, from sur- + baisser to lower, from bas low, from Middle French) + English -ed — more at base
1. : having the curve center below the springing line of imposts
surbased arch
surbased vault
2. : having a surbase