Hiraeth /hɪəraɪ̯θ/ is a Welsh word that has no direct English translation. The University of Wales, Lampeter attempts to define it as homesickness tinged with grief or sadness over the lost or departed. It is a mix of longing, yearning, nostalgia, wistfulness, or an earnest desire for the Wales of the past.
Hiraeth bears considerable similarities with the Portuguese concept of saudade (a key theme in Fado music), Galician morriña and Romanian dor.
(With thanks to The Belle Jar.)