nos·tal·gi·a 
(French “nostalgie”, from Gree “nóstos”, -ou, homecoming + Greek “álgos”, –ous, pain)

feminine noun.

1.          Idealized, and sometimes unreal, longing for moments lived in the past, a time or place.

2.          Melancholy caused by the memory of past joys.

3.          Melancholic state caused by the absence of something or someone.

4.          Melancholic condition caused by the desire to have one’s dreams come true.

5.          Condition of one who is sad, but without apparent reasons.