saddlebag

noun

1. A covered pouch, usually one of a pair, laid across the back of a horse, donkey, or mule behind its saddle, or hanging over the rear wheel of a motorcycle; often made of leather or (on a motorcycle) a rigid material.

   “Frustrated, rushed, you toss the saddlebags filled with textbooks, ungraded papers, and drafts of poems onto the back of your cruiser motorcycle and roar off down Ambler not thinking speed and a strong crosswind will lift the saddlebags into flight like some leather-winged prehistoric bird hanging in the air a second before flopping onto the busiest street in North Abilene.”

   “Lifting the reins over the horse's head, he tied them to a nearby tree limb and moved back to the saddlebags. Untying the leather thongs that bound them behind the saddle, he picked the saddlebags up, hobbled to a nearby tree, and sat down at its base.”

   “There was no camp, bedroll, or fire and no other sign of a man, just the saddled horse with saddlebags and packs tied on behind it.”

2. (broadly, nonstandard)pannier
3. A seat pack or a seat bag (a pouch or a small bag attached to the seat or seat post of a bicycle)
4. (US, in-plural, informal)Loose fatty flesh on a person's upper thighs or buttocks, that hangs like saddlebags.

   “The area treated was always the side of the thighs, where she had visible saddlebags.”

5. A style of house with two rooms separated by a small hall and open space.

verb

1. (transitive)To place in a saddlebag.
2. (transitive)To put a saddlebag on (an animal).