Definition of family silver in US English:

family silver

noun

  • 1Silverware belonging to a particular family, handed down from generation to generation, especially as an heirloom.

  • 2Figurative informal. Something considered to be of great value (materially or otherwise); a precious or venerable legacy. Now chiefly: specifically a well-established company, state-run industry, etc., regarded as an irreplaceable part of a nation's heritage. See to sell (off) the family silver.

Origin

Mid 19th century; earliest use found in Douglas Jerrold (1803–1857), playwright and journalist. From family + silver.