English word liar comes from Proto-Indo-European *lewgʰ-, and later Proto-Germanic *leuganą (To lie, to tell a falsehood.)

Detailed word origin of liar

Dictionary entry	Language	Definition
*lewgʰ-	Proto-Indo-European (ine-pro)	to tell a lie
*leuganą	Proto-Germanic (gem-pro)	To lie, to tell a falsehood.
lēogan	Old English (ca. 450-1100) (ang)
lēogere	Old English (ca. 450-1100) (ang)
lier	Middle English (1100-1500) (enm)
liar	English (eng)	One who tells lies.

Words with the same origin as liar