an anxiety; a worry; a nightmare-like situation
When he finally paid off the mortgage on the house, he felt that he had been relieved of an incubus that had been haunting him for more than twenty years.
in (into, in, on, upon)#cubare (to bend oneself, lie) (Latin)
to wait IN QUE for a BUS is a burden or nightmare. in + cu + bus -- going to college in bus is really a kind of burden.