'pilaster' originates from Italian, specifically the word 'pilastro', where 'pilastro' meant 'pillar or post'.

'pilaster' came into English via Italian 'pilastro' and French 'pilastre', which in turn derive from Late Latin 'pilastrum' and Latin 'pila' meaning 'pillar' or 'heap'.

Initially referring broadly to a pillar or post, it came to mean specifically a shallow, flattened column attached to a wall in architectural usage.