glue and lacquer; inseparable bond
Literary metaphor for an extremely close, inseparable relationship, like glue and lacquer that cannot be separated once joined. The literal meaning 'glue and lacquer' is the basis for the figurative use.
Their friendship is like an inseparable bond of glue and lacquer.
In classical literature, the relationship between husband and wife is sometimes likened to glue and lacquer.
Compound of 膠 (glue) and 漆 (lacquer), both sticky substances that harden and become inseparable when combined. The figurative meaning of a close bond derives from this property.