Which word describes a strong anxiety and unhappiness, often accompanied by a feeling of dread?

The correct answer is "angst." This term specifically captures the complex emotions of anxiety and discontent, particularly the kind that is often existential in nature. "Angst" is rooted in a sense of apprehension or dread, especially concerning one's identity and purpose in life. It evokes a profound emotional state that transcends mere worry, highlighting a deeper, often philosophical struggle.

While "despair" indicates a sense of hopelessness and complete loss of trust or hope, it does not inherently convey the mix of anxiety and apprehension present in "angst." "Melancholy" refers to deep, persistent sadness but lacks the specific connotation of existential dread. "Nostalgia" is a sentimental longing for the past, which suggests a yearning for what once was rather than an active sense of anxiety or dread about the present or future. Therefore, "angst" is the term that best encompasses the feelings described in the question.