Although “derisory” and “derisive” can both mean “laughable,” there are sometimes subtle distinctions made between them. “Derisory” is most often used to mean “worthy of being laughed at,” especially in the sense “laughably inadequate”: “Ethan made a derisory effort to clean the cat box while talking on his cell phone.” Sneering laughter is usually described as “derisive.”
You might more unusually speak of an effort as “derisive,” but most people would think it odd to use “derisory” to describe the tone of someone’s laughter.
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