'unequal-sepalled' originates from English compounds: 'unequal' + 'sepalled'. 'unequal' ultimately comes from Latin 'inaequalis', where 'in-' meant 'not' and 'aequalis' meant 'equal'; 'sepal' comes from Neo-Latin 'sepalum', a 19th-century botanical coinage referring to a floral leaf or segment.

'sepal' was coined in Neo-Latin as 'sepalum' in the 19th century and entered botanical English as 'sepal'; the adjectival form 'sepalled' (having sepals) was formed by adding '-ed', and the compound 'unequal-sepalled' developed in botanical descriptions to specify unequal sepals.

Initially, 'sepal' referred simply to a floral leaf; over time the derived adjective 'sepalled' came to mean 'having sepals', and the compound 'unequal-sepalled' came to mean specifically 'having sepals that differ in size or shape'.