'squirrel' originates from Old French/Anglo-Norman, specifically the word 'esquirel' (or variants such as 'escurueil'), ultimately tracing back to Latin 'sciurus' and Greek 'skiouros', where 'skia' meant 'shadow' and 'ourá' meant 'tail'.

'sciurus' (Greek) became Latin 'sciurus', then Old French/Anglo-Norman forms like 'escurueil'/'esquirel', and through Middle English the word evolved into modern English 'squirrel'.

Initially it meant 'shadow-tailed' (a descriptive compound referring to the tail), but over time it came to denote the specific animal we call a 'squirrel'.