Given to lying; SYN. mendacious.

The deliberate act of deviating from the truth; SYN. prevarication, fabrication.
Deliberately making false statements with the intention to deceive or mislead. Lying may sometimes be justified; for example, for self-protection or to deceive the enemy in wartime.
The question of whether it is ever right to tell a lie has frequently been discussed by moral philosophers, especially with reference to difficult situations, such as whether a doctor should withhold the truth from a patient with a fatal disease or whether one should protect a friend or client with a lie when telling the truth would be a betrayal of confidence.
In pathological lying, the mendacity has no moral justification. The pathological liar is typically an impostor or swindler, adopting a false persona with the aim, say, of obtaining money under false pretences.