liar (n.)

"one who knowingly utters falsehoods," early 13c., from Old English leogere "liar, false witness, hypocrite," agent noun from Anglian legan, West Saxon leogan "be untruthful, lie" (see lie (v.1)). "The form in -ar is probably in imitation of the refashioned forms such as scholar for scoler and pillar for piler" [Barnhart]. A different formation yielded Dutch leugenaar, Old High German luginari, German Lügner, Danish lögner.