means A person who illegally hunts, traps, or fishes for animals on land or in waters where they have no right to take them — or, in cooking, an egg gently cooked in simmering liquid.

from From the verb 'poach,' which carries two threads that may share a root. The older sense comes from Old French 'pochier,' meaning to pocket or bag — to thrust into a pouch — fitting for someone who slips game quietly into a sack. The same word gave us the cooking 'poach' (an egg slipped, like into a pocket, into hot water), and both link back to 'poche,' a pouch or bag, a cousin of the word 'pouch' itself. The illicit-hunter meaning grew from the idea of someone bagging what wasn't theirs to bag.