Cynic

A. adj.
Belonging to or Characteristic of a Sect of humanity called Sentient; distinguished by a capacity to see what exists, to understand what is seen, as well as an equal lack of capacity to understand when not to speak thereof

B. n.
A person disposed to disbelieve in what does not exist, such as sincerity and human goodness, and is wont to express such by an understandable, but inexcusable, lack of tact
(obs) A strange person who sees things only as they are, not as the public would have it be, one who insists on believing all that he sees and hears
(obs) a man who refuses to close his eyes when he sees something which does not exist, nor yet closes his ears when he hears something which cannot have been, but is, spoken
(of animals) a lamb which persists in asking impertinent questions of the leader of the flock, while the flock is being ably led by the butcher or the shearer

Cynicism:
a. An instance of the truth being spoken; a truthful utterance.

Note: There is an (unpardonable) confusion regarding the definition of the cynic and the critic; we note here that the simplest difference between the both pertain to their domain of influence; a Cynic is one who is persistently, if tactlessly, truthful about most issues, a critic is one who is exceedingly truthful in only one aspect only.
The distinction between them maybe likened to that between the rapier and the bludgeon; one who has had the (mis)fortune of encountering the latter rarely, and barely, escapes, while one encountering the latter has enough time on hand to find any handy individual to substitute for oneself, one individual being as good as another for the bludgeon.