Caitiff is pretty rare in contemporary use, but it has functioned since the 14th century as an adjective and also as a noun meaning “a base, cowardly, or despicable person” (as in Shakespeare’s Measure for Measure: “O thou caitiff! O thou varlet! O thou wicked Hannibal!”). Both the adjective and the noun evolved from the Anglo-French adjective caitif, meaning “wretched, despicable.” The French word in turn derived from the Latin captivus, meaning “captive”-the shift from “captive” to “wretched” being perhaps prompted by the perception of captives as wretched and worthy of scorn.
This is a great word to keep in your word quiver. When engaged with a weasel in rhetorical repartee, I imagine pulling out this bolt of a word, cocking my word crossbow, and letting fly.