To be completely worthless or useless; to have little or no value. Refers to farthings (obsolete British units of currency, worth one-quarter of a penny), formerly made from a copper alloy (brass). Primarily heard in UK. I was so excited when my grandfather said he'd give me his car, but this old clunker isn't worth a brass farthing. Over the years working here, I've come to realize that the boss's word isn't worth a brass farthing.

Completely worthless or useless; having little or no value. Refers to farthings, obsolete British units of currency worth one-quarter of a penny that were once made from a copper alloy (brass). Primarily heard in UK. I was so excited when my grandfather said he'd give me his car, but this old clunker isn't worth a brass farthing. Over the years working here, I've come to realize that the boss's word isn't worth a brass farthing.