from The American Heritage® Dictionary of the English Language, 4th Edition
- adv. With the flat side down or in contact with a surface.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adv. With a flat side down or otherwise in contact with a flat surface.
from the GNU version of the Collaborative International Dictionary of English
- adj. With the flat side downward, or next to another object; not edgewise.
from The Century Dictionary and Cyclopedia
- With the flat side downward or next to another object; not edgewise.
flat + -wise (Wiktionary)