haunch
The hip and upper back leg area of a body.
A haunch is the hip and upper thigh area of a person or animal, especially the powerful back legs of four-legged creatures. When a dog or cat sits back on its haunches, it's resting on these strong rear legs with its back upright, kind of like how you might sit on your heels.
The word appears often when describing how animals move or rest. A lion crouching on its haunches before pouncing is gathering all that muscle power in its back legs, ready to spring forward. A rabbit sitting on its haunches while nibbling clover is balancing on those distinctive strong back legs that help it hop.
For people, haunch sounds old-fashioned but means the same hip and thigh area. You might read in a story about a weary traveler squatting down on their haunches to rest by a campfire. The word gives a more physical, muscular sense than just saying “hip” or “thigh.” It reminds us that this part of the body, whether in animals or people, contains some of the strongest muscles we have: the ones that help us run, jump, and move with power.