'square-bottomed' originates from English, combining 'square' (from Old French 'esquarre' and Latin 'quadratus', where 'quadr-' meant 'four' or 'square') and 'bottom' (from Old English 'botm', where it meant 'lowest part'), with the adjectival suffix '-ed' forming the compound adjective.

'square' changed from Old French 'esquarre' (via Anglo-Norman) ultimately from Latin 'quadratus', while 'bottom' changed from Old English 'botm' to Middle English forms such as 'botme' before becoming modern English 'bottom'; the modern compound 'square-bottomed' developed by combining these elements with the suffix '-ed'.

Initially the elements meant 'square' and 'lowest part' respectively; over time the compound has come to mean 'having a bottom that is square in shape' with little change in basic meaning.