Vain indica una ausencia de valor o mérito que puede ser absoluta o relativa <the vain hope that her alcoholic husband would someday give up drinking>.
Idle connota que carece de la capacidad para el uso o el efecto provechoso <she thought it was idle to speculate about how her life might have been different>.
Empty y hollow connotan la ausencia engañosa de auténtica sustancia, solidez, legitimidad o valor <another of the government's empty promises><a hollow victory>.
Unproductive connota no producir resultados, beneficios o ganancias <her search for the missing documents was unproductive>.
