The Latin term “gloria” roughly means boasting, although its English cognate, glory, has come to have an exclusively positive meaning; historically, vain roughly meant futile, but by the 14th century had come to have the strong narcissistic undertones of irrelevant accuracy that it retains today. As a result of these semantic changes, vainglory has become a rarely used word in itself, and is now commonly interpreted as referring to vanity (in its modern narcissistic sense).

-WIKIPEDIA