'non-prestressed' is a modern English compound formed by the negative prefix 'non-' + 'prestressed' (the past-participial/adjectival form of 'prestress'), where 'non-' meant 'not' and 'pre-' meant 'before'.

'prestressed' comes from 'prestress' (formed from 'pre-' + 'stress'); 'pre-' originates from Latin 'prae' meaning 'before', and 'stress' derives ultimately from Old French 'estresse' (from Latin 'strictus', past participle of 'stringere', 'to draw tight'). The compound 'non-prestressed' developed in modern technical English by prefixing 'non-' to 'prestressed' to indicate the negation.

Initially the elements 'pre-' and 'stress' implied 'applying tension/compression before use'; over time 'prestressed' came to be a technical term for structural members with intentionally applied internal forces, and 'non-prestressed' specifically came to mean 'not having such forces applied'.