A business, product, or investment that generates a steady and substantial income reliably over time.
Examples:
- That laundry business you inherited is turning into quite the cash cow.
- The flagship software product became the company's cash cow, funding all other development.
Origin: From the image of a cow that can be milked repeatedly after a single birth; replaced the earlier 'milch cow.'
Synonyms: money spinner, gold mine, steady earner