WordNet sense 1 (freight car without permanent sides or roof):

flatbed, flatcar

WordNet sense 2 (a deflated pneumatic tire):

flat tire

WordNet sense 3 (a suite of rooms usually on one floor of an apartment house):

apartment

WordNet sense 4 (flattened laterally along the whole length (e.g., certain leafstalks or flatfishes)):

compressed

WordNet sense 5 (lacking taste or flavor or tang):

bland, flavorless, insipid, vapid, flavourless, savorless, savourless

WordNet sense 6 (lacking flavor):

tasteless

WordNet sense 7 (not stimulating):

unexciting, unstimulating

WordNet sense 8 (not effervescent):

noneffervescent

WordNet sense 9 (not modified or restricted by reservations):

categorical, unconditional, categoric

WordNet sense 10 (not limited or restricted):

unqualified

WordNet sense 11 ((of taxes) not increasing as the amount taxed increases):

fixed

WordNet sense 12 ((of taxes) adjusted so that the rate decreases as the amount of income increases):

regressive

WordNet sense 13 (sounded or spoken in a tone unvarying in pitch):

monotone, monotonous, monotonic

WordNet sense 14 (characterized by lack of variation in pitch, tone, or volume):

unmodulated

WordNet sense 15 (stretched out and lying at full length along the ground):

prostrate

WordNet sense 16 (not upright in position or posture):

unerect

WordNet sense 17 (having a surface without slope, tilt in which no part is higher or lower than another):

level, plane

WordNet sense 18 (being level or straight or regular and without variation as e.g. in shape or texture; or being in the same plane or at the same height as something else (i.e. even with)):

even

WordNet sense 19 (having or involving or marked by several dimensions or aspects):

multidimensional

WordNet sense 20 (involving two dimensions):

two-dimensional, planar

WordNet sense 21 (collapsed through the release of gas or air):

deflated

WordNet sense 22 (not reflecting light; not glossy):

mat, matt, matte, matted

WordNet sense 23 (emitting or reflecting very little light):

dull

WordNet sense 24 (in a forthright manner; candidly or frankly):

directly, straight

WordNet sense 25 (not progressing or increasing; or progressing slowly):

inactive