Sheep-dip is a strong chemical used to kill insects and other tiny pests that live in a sheep’s wool — lice, ticks, mites, and the like. It is also the special bath, trough, or tank the sheep are run through so the chemical soaks the fleece. Farming word, practical and a little old-fashioned in flavour now, because many places have changed how they treat the animals. The chemical is not mild; farmers are told to wear gloves and keep it off their skin. Though actually, people sometimes stretch sheep-dip in jokes or in other jobs to mean “run the lot through a harsh clean-up,” but the real, ordinary sense is the farm bath and the liquid in it.