under-ˈfloor,v. [under-1 4 a.] trans. To provide with, or form, a floor or under-floor. 1778Phil.Trans. LXVIII. 890 The method of under⁓flooring I have also applied..to a wooden stair-case.1884Coues Key N. Amer. Birds (ed. 2) 155 The basitemporal and parasphenoid bones which underfloor the whole skull.