Antonyms of adj truthful

2 senses of truthful

Sense 1
truthful (vs. untruthful), true -- (expressing or given to expressing the truth; "a true statement"; "gave truthful testimony"; "a truthful person")

untruthful (vs. truthful) -- (not expressing or given to expressing the truth; "the statement given under oath was untruthful"; "an untruthful person")
        => mendacious -- (given to lying; "a mendacious child")

Sense 2
truthful -- (conforming to truth; "I wouldn't have told you this if it weren't so"; "a truthful statement")

INDIRECT (VIA true) -> false -- (not in accordance with the fact or reality or actuality; "gave false testimony under oath"; "false tales of bravery")

Similarity of adj truthful

2 senses of truthful

Sense 1
truthful (vs. untruthful), true -- (expressing or given to expressing the truth; "a true statement"; "gave truthful testimony"; "a truthful person")
       => honest -- (marked by truth; "gave honest answers"; "honest reporting")
       => veracious -- (habitually speaking the truth; "a veracious witness")
          Also See-> honest#1, honorable#1

Sense 2
truthful -- (conforming to truth; "I wouldn't have told you this if it weren't so"; "a truthful statement")
       => true (vs. false) -- (consistent with fact or reality; not false; "the story is true"; "it is undesirable to believe a proposition when there is no ground whatever for supposing it true"- B. Russell; "the true meaning of the statement")