'bacteriopsonin' originates from a combination of elements: 'bacterio-' from Greek 'bakterion' (meaning 'small staff' or 'rod', later used for 'bacteria') and 'opsonin' from Greek 'opson' (meaning 'food' or 'relish'), the latter used metaphorically in immunology to mean a substance that 'makes (microbes) tasty' to phagocytes.

'bacteriopsonin' was formed in medical/biological English by combining the prefix 'bacterio-' with the established immunology term 'opsonin' (coined in early immunological literature). The modern scientific compound reflects this direct combination rather than a long separate phonetic evolution.

Initially the components evoked the literal image 'bacteria + food' (i.e., something that makes bacteria like food to phagocytes); over time it has been standardized to mean 'a serum factor that promotes phagocytosis of bacteria' in immunology.