'downfold' is a compound of English 'down' + 'fold'; 'down' comes from Old English 'dūn' meaning 'down' or 'lower', and 'fold' comes from Old English 'fealdan'/'fold' meaning 'to bend' or 'a bend/fold'.

'down' and 'fold' were combined in Middle English as a descriptive compound (e.g. 'down-fold' or written together) to describe the action or result of folding toward a lower position; over time the compound has been used sporadically in specialized or literal contexts as 'downfold'.

Initially it literally described the physical act or result of folding downward; this basic literal sense has been retained, though the word has remained relatively rare and mainly descriptive.