'apetalousness' originates from Neo-Latin/Modern English, ultimately formed from the adjective 'apetalous' which combines the privative prefix 'a-' meaning 'without' (from Greek) and 'petal-' from Greek 'petalon' meaning 'leaf' or 'thin plate' (hence 'petal').

'apetalous' developed from Greek 'petalon' via New/Medieval Latin formations (e.g. Latinized forms such as 'apetalus') and entered English as 'apetalous'; the noun 'apetalousness' was formed in English by adding the suffix '-ness'.

Initially it referred specifically to being 'without petals' in botanical descriptions; this core meaning has remained stable into modern usage, denoting the condition of lacking petals.