(n.) intense homesickness
When it first appeared in the language in the 1700s, nostalgia was a purely medical term, considered for a long time to be a temporary form of insanity that would seize upon those who had been in unfamiliar surroundings for too long.
Clearly, it is for good reason that nostalgia derives from the Greek word for ‘pain’, algos, and so shares its etymological roots with the likes of neuralgia and analgesia. That original medical meaning weakened over time however, so that by the early 1900s nostalgia had become simply a sentimental longing for home, or for familiar surroundings. In its place, the term nostomania was coined to describe an intense, near crazed or irrational homesickness—but with time, its meaning too has steadily broadened so that today it can be used to describe merely an albeit extreme or intense longing for home.
Both terms also have at their root the Greek word nostos, meaning ‘homecoming’ (or, by extension, ‘the conclusion to a story’).
A less well known synonym for nostalgia—namely patridalgia, or pathopatridalgia—derives from the Latin word for ‘father’, and so literally describes a painful longing for one’s ‘fatherland’.