slug [LME] In medieval times a slug was a slow-moving lazy person, and over time the word came to describe any slow-moving animal or vehicle. For example, the big-game hunter William Baldwin, writing in 1863, described one of his horses as ‘an incorrigible slug’. It has been the term for a slimy snail-like creature since the early 18th century. A slug of whisky, or of lead, is probably the same word, but to slug someone is not, and is related to slog [E19th], and we do not know the origin of either. Sluggard [ME] is based on the rare verb slug, ‘to be lazy or slow’, which may be Scandinavian in origin and which is probably also the source of sluggish [LME], ‘slow and lazy’.