means To injure a joint by wrenching or twisting it so the ligaments stretch or tear, without actually breaking a bone.

from English from around the 1600s, with murky roots — possibly traced back through Old French to the Latin 'exprimere,' to press or wring out, the same wringing motion that twists a joint past its limit. But the trail is faint, and honest dictionaries shrug: the exact ancestry of 'sprain' is genuinely uncertain.