If someone is expressing deep sorrow, which term fits best?

The term "lament" fits best when someone is expressing deep sorrow because it specifically refers to an expression of grief, mourning, or sorrow. It encapsulates the act of openly showing one’s distress and sadness over a loss or misfortune. "Lament" carries connotations of profound emotional pain, often associated with poetry or songs of mourning, thus making it the most suitable choice for conveying deep sorrow.

In contrast, "convey" refers to the act of communicating or transmitting an idea, feeling, or piece of information, which does not inherently suggest sorrow. "Describe" is about detailing or portraying something, but it lacks the emotive depth of sorrow. "Values" pertains to principles or standards of behavior and is unrelated to the expression of emotional states. Therefore, "lament" is clearly the most appropriate choice for indicating deep sorrow.