nostalgia

n. feeling of longing for the past or bygone things, sentimentality

Nostalgia describes a longing for the past, often in idealized form. Nostalgia may or may not also be known as homesickness.
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Nos·tal·gia n. 1. A bittersweet longing for things, persons, or situations of the past. 2. The condition of being homesick; homesickness. [more]Nostalgia - Community and Resources

Noun
1. longing for something past
(hypernym) longing, yearning
(hyponym) homesickness

n. homesickness, nostalgia