sur·based 2 
(sûrbāst′)
(sûrbāst′)adj.
Of or being an arch having a rise less than half its span.
[From French surbaissé, past participle of surbaisser, to flatten : sur-, intensive pref. (from Old French; see SUR-) + baisser, to lower (from Old French baissier, from Vulgar Latin *bassiāre; see ABASE).]