Q. How would you style the past tense of “green-light”—“green-lighted” or “greenlit”?
A. Although Merriam-Webster.com’s dictionary includes the verb “green-light” as a subentry under its entry for the noun form “green light,” it doesn’t conjugate it. But you could consult that same dictionary’s entry for “light” as a verb and choose the first-listed form of the past tense there: “lit” (“lighted” is an equal variant). You might also take a look at Merriam-Webster’s usage note on the subject, which explains that “green-lighted,” once the dominant past-tense form, has recently been losing out to the one-word “greenlit.”
If you’re comfortable getting ahead of recent trends, you could greenlight “greenlit.” If you’re not ready for that, retain the hyphens in the verb forms (“green-light,” “green-lit”). Until Merriam-Webster removes the hyphen from its entry for “green-light” as a verb, that’s what we’d probably do.