'collateral' originates from Medieval Latin, specifically the word 'collateralis,' where 'col-' meant 'together' and 'lateralis' meant 'side.'

'collateralis' transformed into the Old French word 'collateral,' and eventually became the modern English word 'collateral' through Middle English.

Initially, it meant 'side by side,' but over time it evolved into its current meanings of 'security for a loan' and 'secondary.'