Green’s Dictionary of Slang

knacker n.

[SE knacker, a horse-slaughterer]

1. [mid–late 19C] a worn-out horse, fit only for slaughter.

2. [late 19C] by ext. a worn-out, useless person.

3. [1960s] (Aus.) a A$2 bill.

4. [1990s+] (Irish) a general insult aimed at a person.

5. [1990s+] (Irish) a traveller, a tinker.

6. [1990s+] (UK juv.) a thief.