The Oxford English Dictionary is the ultimate authority on the English language:
An act or instance of lying; a false statement made with intent to deceive; a criminal falsehood. Phrase, to tell (†formerly to make) a lie . †Also, without lie, no lie, truly (often as an expletive in Middle English poetry; cf. without fable at fable n. 1d).In mod. use, the word is normally a violent expression of moral reprobation, which in polite conversation tends to be avoided, the synonyms falsehood and untruth being often substituted as relatively euphemistic
The OED sums it up quite nicely. Accusing someone of lying is, violent expression of moral reprobation, which in polite conversation tends to be avoided. Calling someone a liar does not just posses the denotation of accusing them of intentionally attempting to mislead, it possesses the connotation of accusing them of immoral or unethical behavior.
That is all I have to say about that. The Oxford English Dictionary states my points most eloquently.
So you are telling me Oxford only has one definition of the word? Really? Now that would be giving a false statement made with the intent to deceive. Nice going.