'synsepalous' originates from Neo-Latin/Greek compound usage, specifically from the Greek prefix 'syn-' meaning 'together' combined with Neo-Latin 'sepalum' (from Greek roots referring to 'sepal'), where 'syn-' meant 'together' and 'sepalum' meant 'sepal'.

'synsepalous' was formed in botanical Neo-Latin (19th century) as a compound equivalent to 'syn-' + 'sepalous' (from 'sepalum') and entered modern English botanical terminology without major phonetic change as 'synsepalous'.

Initially, it meant 'having sepals joined together,' and this core meaning has remained essentially unchanged in botanical usage.