'nonseptate' is formed from the prefix 'non-' (meaning 'not') + the adjective 'septate', which derives from Latin 'septum' meaning 'partition' or 'divider'.

'septate' entered scientific English via New Latin/Modern scientific usage from Latin 'septum' combined with the adjectival suffix '-ate'; the compound 'nonseptate' arose later in biological descriptions by adding the negating prefix 'non-'.

Initially it designated the simple notion of 'not having septa (partitions)'; this basic meaning has been retained in modern biological usage.