'single-petalled' originates from Modern English as a compound of 'single' and 'petal'. 'single' ultimately traces back to Old French 'sengle' and Latin 'singulus', where 'singulus' meant 'one' or 'single'; 'petal' comes from Greek 'petalon' via French 'pétale' and New Latin 'petalum', where 'petalon' meant 'leaf' or 'thin plate.'

'petal' entered English in the late 18th to early 19th century from French 'pétale' and New Latin 'petalum'; 'petalled' was formed in English as an adjective meaning 'having petals'. 'single' passed into Middle English from Old French and remained as 'single', and the two combined in modern usage to form compounds like 'single-petalled.'

Initially, the Greek root meant 'leaf' or 'thin plate,' and in botanical usage it came to mean 'petal'; 'single' has long meant 'one.' Together the compound came to mean 'having a single layer/row of petals' (as opposed to 'double-petalled') in horticultural contexts.