This is the 2364th most frequent Spanish word.
vano
"Vano" means "vain" or "empty" in English.
Here, 'vano' is used as an adjective meaning 'useless' or 'unsuccessful' in the effort made.
Sus esfuerzos fueron en vano.
His efforts were in vain.
In this case, 'vano' refers to the architectural term for an open space or an opening such as in a wall or door.
El vano de la puerta es muy estrecho.
The door opening is very narrow.
Here, 'vano' is employed as an adjective denoting 'excessive' or 'conceited' enthusiasm, implying insincerity or overstatement in the behavior.