'cleistogamous' originates from New Latin/Modern scientific coinage and ultimately from Ancient Greek, specifically the Greek elements 'kleistos' meaning 'closed' and 'gamos' meaning 'marriage' (joined), where 'kleistos' meant 'closed' and 'gamos' meant 'marriage/union'.

'cleistogamous' derived via New Latin (formation from Greek roots) from Greek 'kleistos' + 'gamos' and entered English in scientific usage to describe 'closed-married' (i.e., closed, self-fertilizing) flowers, eventually becoming the English adjective 'cleistogamous'.

Initially formed from elements meaning 'closed' + 'marriage' (a literal 'closed union'), but over time it came to be used specifically for flowers/plants that remain closed and self-pollinate (the modern biological sense).