Meaning
Be thoroughly knowledgeable or competent in a subject. The possessive normally changes with the subject: know my, your, his, her or their onions. Regional use: Now chiefly old-fashioned British English; originated in American English.
Origin
Despite its present British flavour, the expression is first recorded in the United States in 1922. It belonged to a 1920s family of playful formulas such as 'know your oats' and 'know your apples'. The theory linking it to lexicographer C. T. Onions is a later folk etymology.
Research Sources
References used to check this entry’s meaning, history, or documented forms.
Variants
- Know one's onions
- Know your onion
Usage Examples
- Ask Priya about the old heating system; she really knows her onions.
- The conservator knew his onions and identified the repair before opening the case.