disparate describes things essentially different in kind — so unlike that comparison does not hold — and, of a single body or collection, one made up of fundamentally different and often incongruous elements.
The two senses work at different scales. Applied to several things, it denies them common ground: disparate accounts of an event are not merely conflicting but built on premises that do not meet. Applied to one thing, it describes internal composition, as in a disparate coalition or a disparate body of evidence. Either way the word claims more than different does. Things that differ in degree are not disparate; things that differ in category are. This is why various and diverse, which imply range inside a shared class, are weaker substitutes — they assume the class that disparate refuses.
American anti-discrimination law uses the word as a term of art, where disparate treatment means deliberately unequal handling and disparate impact means a neutral policy that falls unequally in practice. That legal usage leans on the older sense of unequal rather than the modern sense of incommensurable.
The word entered English around 1600 from the Latin disparatus, past participle of disparare, "to separate, divide," from dis-, "apart," and parare, "to prepare, procure." Its sense was shaped in parallel by the Latin dispar, "unequal, unlike," from par, "equal" — the same root as parity and compare. The two ancestries explain the word's double pull between "kept apart" and "not matched," and the legal usage above sits on the second. The library's entry for 📝wit turns on the same tension, defining it partly as the ability to relate seemingly disparate things.