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Definitions

ill-founded

[il-foun-did] / ˈɪlˈfaʊn dɪd /
ADJECTIVE
invalid
Synonyms
STRONGEST
baseless false inoperative irrational null unfounded unreasonable unscientific unsound untrue
STRONG
bad void wrong
WEAK
fallacious illogical mad not binding not working nugatory null and void reasonless sophistic unreasoned
Antonyms
STRONGEST
honest logical reasonable sensible sound true valid
STRONG
OK good right
WEAK
worthwhile worthy

From Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.