What does Job mean by "miserable comforters"?

In Hebrew the phrase is two words: comforters, a form of nacham, and amal, which Brown-Driver-Briggs gives as "trouble, labor, toil" (tap comforters, miserable). It is the word of the last verse of Eliphaz's speech, just before: "They conceive mischief and produce iniquity" (15:35), where mischief is amal. Job says what he wanted instead: "I would strengthen you with my mouth. The solace of my lips would relieve you" (16:5). He had said before, "To him who is ready to faint, kindness should be shown from his friend" (6:14). The friends had come "to sympathize with him and to comfort him" (2:11), and had sat with him seven days and seven nights, "and no one spoke a word to him, for they saw that his grief was very great" (2:13). The book doesn't say in this chapter whether Job's word for them is fair; the LORD's own word on the friends comes at the book's end (42:7-8).