Main entry: effortless
Definition: requiring or apparently requiring no effort
Usage: the swallows glided in an effortless way through the busy air
Antonyms: effortful
Definition: requiring great physical effort
Main entry: effortless, casual
Definition: not showing effort or strain
Usage: a difficult feat performed with casual mastery; careless grace
Definition: not easy; requiring great physical or mental effort to accomplish or comprehend or endure
Antonyms: uneasy
Definition: lacking a sense of security or affording no ease or reassurance