'interrelation' originates from the prefix 'inter-' meaning 'between' and the root 'relation' from Latin 'relatio', meaning 'a bringing back'.

'relatio' transformed into the Old French word 'relacion', and eventually became the modern English word 'relation', which combined with 'inter-' to form 'interrelation'.

Initially, it meant 'a bringing back between', but over time it evolved into its current meaning of 'the way in which two or more things or people are connected'.