'nonconscious' is formed in English from the negative prefix 'non-' (from Latin 'non', meaning 'not') + 'conscious'. 'conscious' traces back to Latin 'conscius' (from 'con-' together + 'scire' to know).

'conscious' came into English via Latin 'conscius' and Old French forms (e.g. 'conscient'), becoming Middle English 'conscious', after which the productive English prefix 'non-' was attached to form 'nonconscious' in the 19th century and later the adverb 'nonconsciously'.

Originally built simply to mean 'not conscious' (i.e., lacking consciousness); it has retained that core sense but is now used more broadly in psychology and everyday usage to describe actions or processes occurring without conscious awareness.