Q. Per paragraph 7.92 in CMOS, some compound adjectives keep a hyphen even after a noun, including compounds with “ill” (also covered under “ill” in the hyphenation table). For example, we could be correct in writing this: “The scene was ill-described.” In cases where the compound is not in play, I assume we stick to dropping the hyphen, since we’re now working with just an adverb + verb. For example: “Gruesome ill described the scene.” Is this correct? I suspect I’m overthinking things. (Revising the sentence beyond mechanical correctness is out of the question in this client’s case.)
A. Though CMOS doesn’t cover this specific case, common sense does suggest that you wouldn’t need a hyphen when an adverb is paired with a past participle used as a verb rather than as an adjective. You could try substituting a different adverb for ill to test this hunch: “Gruesome now described the scene.” A hyphen would be out of place there.
But the wording in your sentence is unusual—ill is rarely paired with verbs other than afford, treat, or use—so hyphenation might be helpful. The expression ill afford is in Merriam-Webster without a hyphen, but that phrase generally has only one form: can (or could) ill afford. By contrast, both ill-treat and ill-use are entered as hyphenated verbs, giving you a couple of models to follow.
Verdict? A hyphen in your example, though not strictly required (see also CMOS 7.96, sec. 2, under “phrases, verbal”), may help clarify that ill belongs with the verb. You could add one (“Gruesome ill-described the scene”) unless your client prefers otherwise.