Folks,I need yor help.I am stuck on a word that is vanity.In the sentence of "The poet used to warn of the vanity of mental ambition."According to Longman Dictionary which is for ESL students,one of the explanations is"lack of importance of something compared to other things that are more important."Imight be a little slow on the uptake please help me to be illucidated on that.

The poet used to warn of the vanity of mental ambition."

One meaning of vanity that would seem to make sense in this context is "futility, pointlessness."

Regardless of the warning about mental ambition, I shall add here the latin root of "vanity", which is vanus meaning empty. In the example given, vanity thus means emptiness of purpose or of substance.

"lack of importance of something compared to other things that are more important."

I am, rather, stuck on this definition; it exhibits none of the mental ambition the poet warned of--or perhaps too much. I leave it to you all to determine whether this observation or that definition exhibits more of the absolute lack of importance.

"Vanity of Vanities, saith the Preacher,
vanity of vanities, all is vanity." (Ecclesiastes 1:2)./ ...
That is one answer I got by using Google using "Vanity, Vanity, all is vanity."
Got pages of answers but one with the Bible reference in the lead line has quite a bit of information.
wow