Late Middle English (in an earlier sense). From Middle French, French mensonge lie from a vulgar Latin form approximating to *mentionica from post-classical Latin mention-, mentio lie + -ica.
Definition of mensonge in US English:
mensonge
nounˌmɒnˈsɒn(d)ʒ
rare
A lie, a tall story.
Origin
Late Middle English (in an earlier sense). From Middle French, French mensonge lie from a vulgar Latin form approximating to *mentionica from post-classical Latin mention-, mentio lie + -ica.