'isosepalic' originates from Greek prefix 'iso-' (from Greek 'isos') meaning 'equal' and from New Latin 'sepalum' meaning 'sepal' (a floral part), where 'iso-' meant 'equal' and 'sepalum' referred to the sepal.

'isosepalic' was formed in modern botanical English by combining the prefix 'iso-' with the element 'sepalic' (from 'sepal'/'sepalum'), modeled on related botanical adjectives such as 'isosepalous'; the formation and use date to botanical descriptions from the 19th–20th century.

Initially the components literally conveyed 'equal sepal/covering', and over time the combined term came to be used specifically in botany to mean 'having sepals of equal size or shape'.