The tarsus is the ankle — more exactly, the group of seven small bones that sit between your lower leg and the long bones of your foot. It is the part of the foot that takes your weight when you land, and it lets your foot turn and tilt. In careful medical English, 'the tarsus' names the whole group and 'a tarsal' names one bone of it. The plural is 'tarsi' (TAR-sigh), following the Latin. Like 'tarsal', this is a clinical or scientific word, not a word for describing a sore foot to a friend. You will also meet it outside human medicine: in birds and insects, 'tarsus' names a segment of the leg or foot, so biologists and birdwatchers use it constantly — a birdwatcher may measure a bird's tarsus to identify the species. And there is the eyelid meaning again: the tarsus of the eyelid is the firm plate of tissue that holds the lid's shape, which is why an eye surgeon says the word as often as a foot doctor does. Note also, quite separately, that Tarsus is a real city in southern Turkey, known as the birthplace of St Paul — same spelling, unrelated history.