Chattel and cattle are the same word, and so is capital. All three descend from Late Latin capitale, "property, stock," from capitalis, "chief," literally "of the head," from caput, "head." Chattel came through central Old French chatel in the early 1200s; cattle came through Old North French catel, the Norman form of the identical word.
So this is another Norman-versus-Parisian pair, like warden and guardian or catch and chase, except that here the two forms diverged in meaning rather than in job description: cattle narrowed to livestock, chattel stayed as a general legal term for movable property. Its application to enslaved people dates from the 1640s, and the phrase chattel slavery later became a rhetorical instrument of the abolitionists — a use that turns the word's own history, property measured by the head, into an accusation.
chattel (n.) early 13c., chatel "property, goods," from Old French chatel "chattels, goods, wealth, possessions, property; profit; cattle," from Late Latin capitale "property" (see cattle , which is the Old North French form of the same word). Application to slaves is from 1640s and the word later became a rhetorical figure among the abolitionists. also from early 13c.