'neutral-smelling' is a compound formed from 'neutral' + the present participle 'smelling' (from the verb 'smell'). 'neutral' originates from Latin, specifically the word 'neutralis' (from 'neuter') meaning 'neither of two'; 'smell' originates from Old English 'smellan' referring to emitting an odor.

'neutral-smelling' is a Modern English compound; 'neutral' passed into English via Old French and Middle English from Latin 'neutralis', while 'smell' existed in Old English as 'smellan' and became the modern verb 'smell'; combining them produced the descriptive compound now written as 'neutral-smelling'.

The element 'neutral' originally meant 'neither of two' and more generally 'not taking sides'; in compounds like 'neutral-smelling' its meaning shifted to indicate absence of a distinguishable (positive or negative) odor — i.e., 'no noticeable smell'.