Roget's Thesaurus of English Words and Phrases by Peter Mark Roget

251. Flatness — N. flatness &c adj.; smoothness &c 255.

plane; level &c 213; plate, platter, table, tablet, slab. V. render flat, flatten; level &c 213. Adj. flat, plane, even, flush, scutiform†, discoid; level &c (horizontal) 213; flat as a pancake, flat as a fluke, flat as a flounder, flat as a board, flat as my hand.