Joining in a short expression two words of opposite meaning, such as "sweet bitterness".
In The Posthumous Memoirs of Brás Cubas
It was fear, and it was not fear; it was pity, and it was not pity; it was vanity, and it was not vanity; in short, it was love without love, that is, without delirium
"Love without love" joins in a short expression the affirmation and the negation of the feeling, and "that is, without delirium" explains what is missing from the love that remains.
Chapters CI to CXVI: The Wall, the Weld, and the Old Leaves, the narrator