Yes it's an English word no, nobody uses it.

A lier would something or someone lying in a horizontal position. However, I wouldn't say it's used. I can't say I've ever read it or heard it and Google yields few results. It is common as part of the word 'outlier' though.

Interesting that other English speakers are commenting that nobody uses it. I'm from Western Canada, and we use it often to refer to someone who habitually lies.

I don't believe it's an English word. So I'm going to check a dictionary. It's not in the American Heritage dictionary. Wait: I was wrong. it IS in the Merriam-Webster Third, Unabridged. "Lier (1): one that lies (as in ambush). Lier (2), archaic: var of LEHR." The people who are most likely to say "Is that a word?" are Scrabble players, and there is a special dictionary for Scrabble players. It's compiled by Merriam-Webster for the company that manufactures the Scrabble game. According to the Official Scrabble Players' Dictionary, Sixth Edition. And it's in there, too. "LIER  n  pl. LIERS one that lies or reclines." It's also in the competing Scrabble authority, the "Tournament Word List." So I guess it is a real English word, and it is legal to play in Scrabble. However, I haven't been able to find any examples of real use. I don't think you should use it, because it is very rare, and almost everyone who reads it will think it is a misspelling of "liar."

i have never used it