'pentyl' originates from 'International Scientific Vocabulary', specifically from 'penta-' meaning 'five' and '-yl' denoting a radical derived from a hydrocarbon.

'pentyl' was formed in the 19th century as chemists named hydrocarbon radicals systematically, and eventually became the modern English word 'pentyl'.

Initially, it meant 'a five-carbon alkyl radical', and this meaning has remained the same in modern usage.