'effortlessness' is formed in modern English by adding the noun-forming suffix '-ness' to the adjective 'effortless'. 'Effortless' itself is formed from the noun 'effort' + adjectival suffix '-less' ('without').

'effort' was borrowed into English from French 'effort' (16th–17th century). The adjective 'effortless' developed from the compound of 'effort' + '-less' in English, and later the abstract noun-forming suffix '-ness' produced 'effortlessness'.

Originally 'effort' meant 'exertion' or 'strain'; 'effortless' then meant 'without exertion', and 'effortlessness' came to denote the quality or state of being without exertion or appearing easy.