Adjective effortless has 2 senses
  1. effortless - requiring or apparently requiring no effort; "the swallows glided in an effortless way through the busy air"
    effortful, backbreaking, grueling, gruelling, hard, laborious, punishing, toilsome, dragging, exhausting, tiring, wearing, wearying, heavy, labored, laboured, labor-intensive, labour-intensive, leaden, plodding, arduous, straining, strenuous, difficult, Sisyphean
  2. casual, effortless - not showing effort or strain; "a difficult feat performed with casual mastery"; "careless grace"
    Antonyms: difficult, hard (indirect, via easy)