There is a single word to describe people with a lack of honesty: liar. Is there an equivalent single word to describe an honest person?
The word must be a noun and not an adjective. The are obviously many adjectives that describe people who tell the truth. I am looking for something somewhat like the Spanish word, verdadero.
In a word, the answer is "no". In the same way there is no direct antonym for murderer, thief, car-jacker, etc.
Saying that, there did use to be a word: Soothsayer. (In the mid-14th century it meant, "one who speaks truth".)
Straight-shooter comes to mind.
I cannot think of a simple antonym for liar. This thread postulates that this is because there is no absolute condition for truth.
Idealistically, one assumes that another is always telling the truth, and if he is not telling the truth he becomes a liar. In essence, we may prescribe that telling the truth is a "normal" behavior and thus a word has not been given to describe it. Similarly, there are no simple antonyms for killer or robber.
In logic puzzles about people who always lie and people who always tell the truth (of which there are many), the latter are usually called truth-tellers. However, sometimes one finds in that context truthers, a word that has since come to mean something else also.
Candid? As in: "He's a perfectly candid fellow; he told the Emperor exactly what he thought of his new wardrobe." Frank would also work there.
Interesting question. A person can be characterized as being a "truth teller" or an "honest broker," a "reputable source" who is "believable" and possesses "veracity." There appears to be no single noun - in common use, anyway - that captures the idea.
Adjectively, however, we have many choices. A person can be genuine, straight forward, sincere, frank, honorable, etc.
I think it's fine to use truth-teller itself.
The first rule of philosophical discussion (and from the comments, we are having a philosophical discussion) is to define your terms.
Our quodlibet here is not "that which has not yet been named," but the liar to which we are proposing an opposite.
There is not a simple sense of a liar which is has a unanimous, agreed upon meaning in all circumstances. In this case, determining an antonym becomes difficult.
A liar is someone who has told a lie.
A liar is a person who has habitually told lies.
A liar is a person who usually tells lies.
A liar is a person who can't tell the truth.
A liar is a person who can't tell the truth in particular "important" contexts.
A liar is someone who has told a lie in a particular, "important" context (priestly initiation, marriage, job interview).
A liar is someone who has told a lie that is known to be a lie.
A liar is someone who has told a lie, whether the subject of the lie is a justified belief on the part of the liar or not.
A two-year-old, with developing cognitive and moral abilities, is a liar whether by "intent" or "accident".
A liar is someone who has told a lie, whether by intent or accident.
A liar is someone who has told a lie, whether by omitting the full truth or deliberately obscuring it.
A liar is anyone who has said anything "defininitive" except for the most trivial of statements, given the messy way that human brains deal with propositions, conflicting desires and loyalities, and the overloaded meanings that things in the real world have.
A liar is a robot with a broken truth-telling module.
A liar is someone who tells lies to me, repeatedly, during the period of our acquaintence.
A liar is a person who tells "little white lies" .
A liar is a person who tells "little white lies" habitually, with an occasional targeted lie to their significant other, employer.
A liar is a person who tells their lover, spouse, significant other, "I love you," without really knowing whether they mean it, on at least one day a month.
A liar is a person if their Diety has determined them to be a liar, according to The Rules.
A liar is the opposite of a whistle-blower, whether by actively covering up the truth of some circumstance, event, or condition, or by failing to communicate it to those who might be affected.
What's the opposite of a "liar"?
As a single answer, a flexible word is about the only thing that can work here. That, or multiple words for different antonymic senses.
Why not truth-teller?
I'm deriving some of this from my earlier comments and discussion around them.
My initial definition of truth-teller from the 1913 edition of Webster's was "One who tells the truth."
The two criticisms I've seen are that the term isn't contemporary, or that it's not a "single word".
I believe that it is certainly in current usage. (Certainly more so than soothsayer, even though soothsayer can also mean "truth-teller".)
Here are some usage examples from print:
Larry Summers: a Truth-Teller ...
[...] there’s something refreshing about his persona as a truth-telling curmudgeon who’s equally honest about himself.
Ironic usage: The Washington Post, “Bill Kellers wrongheaded attack on HuffPo”
Indeed, just yesterday, HuffPo prominently linked to a great Times story debunking many of the claims of bold truth-teller Chris Christie.
Helene Cooper, The House at Sugar Beach
I would then return to Liberia a conquering hero, a famous journalist, a truth-teller extraordinaire.
Mark Clark Review of State of Play
"If there’s a hard sell in our day to day lives it’s the concept of the heroic journalist, the character State of Play director Kevin MacDonald calls his ‘truth-teller’.
There are more examples from twitter, from google books, from titles on Amazon, etc..
The accepted answer, soothsayer is as much a compound as truth-teller is. It also has the sense of 'fotune--teller' -- someone who can divine the truth, not necessarily someone who speaks truth consistently. This may be the sense intended by the OP, but isn't what I would consider the opposite of a liar.
Straight-shooter (from @Kevin) is another nice compound, which has in some cases overlapping meaning with some cases of truth-teller.
As @msh210 points out, truth-teller has had a technical usage in logic puzzles for a long time -- simply meaning "someone who always tells the truth," as opposed to the liar, who always lies (or gives not p when the truth is p).
But in common parlance, the word truth-teller usually means someone who speaks the truth in difficult circumstance, or tells "truths" which are widely unpopular (within some related constituency).
Adjective, not a noun, but Honest.
Blunt and undiplomatic are words that can be used when the truth is not exactly a welcome thing. Candid is similar but less so.
Adjective, not a noun, but unimpeachable?
Here are a few negative ones: rat, fink, snitch, mole, loose cannon, tattletale, traitor, blabbermouth.
A not so negative one: critic. "He was my friend and critic" means he didn't lie about things to make me feel good.
Someone who gives information: informer, informant. (This is presumed true, otherwise he or she is a misinformer, not an informer.)
It's all about what/whose truth you tell to whom, in what role.
Also: reporter. (A reporter gives a truthful, if subjective, account; a lie is not a report.)
Announcer.
Inspector. (Determines the truth of a situation, and relays.)
The word "witness" sometimes implies telling the truth. A witness can lie, but is then "bearing false witness" or may be a "hostile witness". In the absence of these situations, a witness is presumed to be telling the truth. Another use of the word: Jehovah's Witnesses believe they are spreading the truth, which is probably part of the reason why they chose that name for themselves.
A voice that tells a story: narrator. A narrative may be fictional, but that isn't the same thing as a lie. A narrator for a documentary or true story is a truth-teller.
Advisor.
Confidant. More like someone who guards the truth, but it goes hand in hand with honesty. Someone who lies to you is probably not suitable for a confidant/e!
Intimate (noun).
Try also blunt speaker, plain speaker, forthright person, outspoken person, someone who tells it like it is, someone who calls it like he sees it.
There is also honest broker (used of someone acting as an intermediary).
Incidentally, what's the deal with so many people wanting one-word descriptors for what are often quite complex or significantly context-bound concepts? Multi-word nouns exist for good reason.
No, there won't be a word to mean truth-teller. Or a perfect antonym of liar.
One is expected to speak the truth, by default. When everyone is supposed to be honest, a liar is an exception.
Only when liars become the predominent majority do we need to coin a word/ neologism for the honest.
