'sub-discipline' originates from Latin prefix 'sub-' and the noun 'discipline'. Specifically, 'sub-' (Latin) meant 'under, below' and 'discipline' comes via Old French from Latin 'disciplina', where 'disciplina' meant 'teaching, instruction'.

'discipline' changed from Latin 'disciplina' to Old French 'discipline' and then into Middle English as 'discipline'. The prefix 'sub-' (Latin) was later combined with 'discipline' in modern English to form the compound 'sub-discipline'.

Initially, the elements meant 'under' (sub-) and 'teaching/instruction' (disciplina); over time the compound came to mean a 'distinct, narrower branch within a larger field' rather than literal 'under instruction'.