'preexist' originates from Latin elements, specifically from the prefix 'pre-' (via Latin 'prae-' meaning 'before') combined with the verb 'exist' (from Latin 'existere'), where 'prae-' meant 'before' and 'existere' meant 'to stand forth; to exist'.

'preexist' developed from Late Latin/Medieval Latin formations such as 'praeexistere' or related compound forms and eventually entered modern English as the prefixation of 'pre-' to 'exist', yielding 'preexist'.

Initially it conveyed the idea 'to stand forth or exist before' and over time it has retained that sense, now commonly meaning 'to exist beforehand' or 'to exist prior to something else'.