IPA: /ˌmɪθəʊˈmeɪniæk/
KK: /mɪθəˈmeɪniæk/
A person who has a tendency to lie or exaggerate, often creating false stories or myths.
The mythomaniac told incredible tales that no one believed.
Mythomaniac → It is formed from "mythos" (from Greek, meaning story or myth) and "mania" (from Greek, meaning madness or obsession). The word describes a person who has an obsession with myths or lies.
Think of someone who is obsessed with 'stories' ('mythos') and has a 'madness' ('mania') for them — that's what a mythomaniac is.