Saudade...

Wikipedia definition for saudade:

Saudade is generally considered one of the hardest words to translate. It originated from the Latin word solitatem (loneliness, solitude), but developed a different meaning. Loneliness in Portuguese is solidão (a semi-learned word), from Latin solitudo. Few other languages in the world have a word with such meaning, making saudade a distinct mark of Portuguese culture. It has been said that this, more than anything else, represents what it is to be Portuguese.