das Heimweh
homesickness
The feeling of longing for home, family, or familiar surroundings when you are in an unfamiliar place.
Nach drei Wochen im Ausland bekam sie schreckliches Heimweh.
After three weeks abroad, she became terribly homesick.

homesickness
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homesickness
The feeling of longing for home, family, or familiar surroundings when you are in an unfamiliar place.
Nach drei Wochen im Ausland bekam sie schreckliches Heimweh.
After three weeks abroad, she became terribly homesick.

The word consists of 'Heim' (home) and 'Weh' (an old word for pain). So 'Heimweh' (homesickness) is literally 'home pain' or longing for home.
Das Gefühl von Heimweh kann sehr stark sein.
The feeling of homesickness can be very strong.
'Heimweh' (homesickness) is usually used with the verbs 'haben' (to have), 'bekommen' (to get), or 'leiden unter' (to suffer from). You cannot say 'Heimweh sein'.
Am Anfang hatte ich starkes Heimweh.
At the beginning, I was very homesick.
To describe the strength of the feeling, you use adjectives such as 'starkes' (strong), 'großes' (great), or 'schreckliches' (terrible) Heimweh.
Als Austauschschüler hatte er anfangs großes Heimweh.
As an exchange student, he was very homesick at first.
longing
'Sehnsucht' and 'Heimweh' both have to do with missing something. 'Sehnsucht' is the more general word: it can be directed toward many things, for example a person, a place, peace and quiet, or a different life. 'Heimweh' is more specific. It means homesickness, or longing for home, family, or familiar surroundings when you are somewhere else. Learners may confuse the words because Heimweh is a form of Sehnsucht. When it is clearly about home or one's homeland, 'Heimweh' is more natural. In all other cases, 'Sehnsucht' usually fits better.

Im Ferienlager bekam Tom am ersten Abend starkes Heimweh.
At the holiday camp, Tom became very homesick on the first evening.
Nach dem langen Arbeitstag hatte sie Sehnsucht nach Ruhe und einem Spaziergang.
After the long workday, she longed for peace and quiet and a walk.