6
featureless(adjective, continuous)
6
final(adjective, absolute, positive)
6
flatcar
6
floor(noun, level, story, bottom, deck)
6
habitation(noun, place, house, home, box)
6
hollow(noun, adjective, dull, deep, space)
6
inactive(adjective, dull, quiet, slow, heavy)
6
inane(adjective, dull, stupid, lackluster)
6
indubitable(adjective, absolute, positive, categorical)
6
joint(noun, place, informal, base, house)
6
lusterless(adjective, light, excite)
6
monotone(adjective, dull, dark, gloomy, ordinary)
6
muddy(adjective, dark, cloudy, colors)
6
quarters(noun, territory, place, base, range)
6
residence(noun, place, base, house, home)
6
roost(noun, place, base, house, home)
6
run-of-the-mill(adjective, dull, set, silly, common)
6
short(adjective, low)
6
steady(adjective, calm, quiet, strong, smooth)
6
still(adjective, dull, quiet, soft, gentle)
10 years ago|55k views|share |citing 
APASmart Define. (2016). flat thesaurus. Retrieved September 20, 2026, from https://smartdefine.org/flat/thesaurus/synonyms
ChicagoSmart Define. 2016. "flat thesaurus" https://smartdefine.org/flat/thesaurus/synonyms (accessed September 20, 2026).
HarvardSmart Define 2016, flat thesaurus, Smart Define, viewed 20 September, 2026, <https://smartdefine.org/flat/thesaurus/synonyms>.
MLASmart Define. "flat thesaurus" 1 March 2016. Web. 20 September 2026. <https://smartdefine.org/flat/thesaurus/synonyms>