n. 25B6; noun
a smack on the rump : REAR (END), seat; buttocks, cheeks; Brit. bottom; informal backside, behind, BTM, sit-upon, derrière; Brit. informal bum, botty, jacksie; N. Amer. informal butt, fanny, tush, tail, buns, booty, heinie; humorous fundament, posterior, stern; Anatomy nates.
the rump of the army : REMAINDER, rest, remnant, remains.