'haphazardness' is formed in modern English by adding the noun-forming suffix '-ness' to the adjective 'haphazard', creating the meaning 'the state or quality of being haphazard'.

'haphazard' itself arose in Early Modern English (c. 16th–17th century) as a compound of 'hap' + 'hazard'; 'hap' meant 'chance, luck' and 'hazard' referred to a risk or game of chance. Over time 'haphazard' became the standard adjective, and later '-ness' was added to make the noun 'haphazardness'.

Originally the elements implied 'by chance' (i.e. 'hap' + 'hazard'), and the compound meant something that occurred by chance; it evolved to describe things done without planning or order, and 'haphazardness' names that quality.