'over-scrupulous' is a compound formed from the prefix 'over-' and the adjective 'scrupulous'. 'Over-' originates from Old English 'ofer', meaning 'above' or 'beyond' (used here to denote excess). 'Scrupulous' originates from Latin 'scrupulus', a diminutive of 'scrupus', meaning 'small sharp stone' (metaphorically used for a prick or anxiety of conscience).

'scrupulus' in Latin gave rise to Late Latin/Old French forms and entered Middle English as 'scrupulous' meaning 'having scruples, conscientious'. The prefix 'ofer' in Old English developed into modern English 'over' and was combined with 'scrupulous' to create 'over-scrupulous' to indicate an excessive degree of scrupulousness.

Originally 'scrupulous' referred to a sense of conscience or troubling doubt (like a 'prick' of conscience). Over time it meant 'conscientious' or 'careful about moral correctness'. 'Over-scrupulous' later developed to mean 'excessively' or 'unduly' scrupulous—i.e., going beyond reasonable conscientiousness.