solder: [14] To solder something is etymologically to make it ‘solid’. The word was originally acquired, as a noun, from Old French soldure, a derivative of the verb solder ‘solder’. This in turn came from Latin solidāre ‘make solid, strengthen, fasten’, a derivative of solidus ‘solid’ (source of English solid). => soldier, solid[solder etymology, solder origin, 英语词源]