Truthful means honest or believable. A truthful answer to a question doesn’t mince words—it is completely straightforward and accurate.
If your little sister asks you whether the Tooth Fairy is real, you’ll have to consider how truthful you want to be. You can think about whether the truthful answer will be to upsetting for her, since you’re not under oath in a courtroom, where you’re legally obligated to be truthful. A now-obsolete adjective with the same meaning was truthy, “characterized by truth.”
expressing or given to expressing the truth“gave
conforming to truth“a
trueconsistent with fact or reality; not false