An Etymological Dictionary of Astronomy and Astrophysics

1. That part of a room, hallway, or the like, that forms its lower enclosing surface and upon which one walks.
   

2. A level, supporting surface in any structure (Dictionary.com).

Etymology (EN): M.E. flor, from O.E. flor (cf. M.Du. vloer, M.H.G. vluor, Ger. Flur “field, meadow”), from PIE *plaros, from *pele- “flat; to spread.”

Etymology (PE): Kaf “floor; plain ground.”