The term "knacker" has several meanings, depending on its context.
1) In British English, a knacker is an animal slaughterer or butcher who specializes in horse meat. This usage comes from the Old English word "cnyppan," meaning to kill or slaughter.
2) In Irish and Scottish dialects, "knacker" can refer to someone who is lazy or idle. The term may have originated from the idea of a knacker being someone who kills animals for a living, which was seen as an undesirable job.
3) In some parts of Ireland, "knacker" can also be used as a term of affection or endearment, similar to how people in other cultures might use terms like "honey," "sweetheart," or "darling."