trasero
/tɾaˈseɾo/ · A2 · adj
back, back-side, rear end, posterior
🍑 tras (behind) + -ero: the thing that is behind
From tras, meaning behind or after, as in detrás and atrás. The suffix -ero makes it the behind one. As an adjective it means rear (la puerta trasera = the back door); as a noun, el trasero is a polite word for the butt.