The Spanish word 'saldo' meaning 'balance' or 'remainder' comes to Spanish through Italian 'saldo', which ultimately derives from Latin 'solidus' meaning 'solid' or 'whole'. The semantic evolution from 'solid/whole' to 'balance/remainder' likely developed through the concept of settling accounts or making something complete or whole in financial transactions.

Some related Spanish words include 'sólido' (solid), which comes from the same Latin root 'solidus'. The connection between 'saldo' and 'sólido' reflects how a financial balance represents the solid, final figure in an accounting context.

English speakers might recognize the connection to words like 'solid' and 'soldier' (which originally meant someone who was paid in solid coins), both of which come from the same Latin root 'solidus'. The word 'solder' (to join metals together) is also related, referring to making something solid or whole. These words share the core concept of something firm, whole, or complete, though 'saldo' evolved specifically toward financial meaning in Spanish.