'benzylpenicillin' originates from a combination of 'benzyl' (from chemical nomenclature ultimately tied to 'benzene' plus the suffix '-yl', used to denote a radical) and 'penicillin' (from Latin 'penicillus'), where 'benzyl' meant 'a radical derived from benzene' and 'penicillus' meant 'little brush' or 'brush-like'.

'penicillin' was named after the fungus Penicillium (from Latin 'penicillus' meaning 'little brush') because of its brush-like conidiophores; after Alexander Fleming discovered the antibiotic effect in 1928 the substance isolated and characterized as 'penicillin' became the drug name. The specific chemical form 'benzylpenicillin' (penicillin G) was later identified and the combined term reflects the benzyl-derived form of penicillin.

Initially the root referred to the brush-like fungus structure ('penicillus'), but over time 'penicillin' came to denote the antibiotic substance derived from that fungus; 'benzylpenicillin' specifically denotes the benzyl (G) form of that antibiotic.