Antonyms of adj untruthful

1 sense of untruthful

Sense 1
untruthful (vs. truthful) -- (not expressing or given to expressing the truth; "the statement given under oath was untruthful"; "an untruthful person")

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")

Similarity of adj untruthful

1 sense of untruthful

Sense 1
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")
          Also See-> dishonest#1, dishonorable#2