Airy fairy

Now means fanciful, vague or unrealistic and in this construction was coined by Tennyson (1809-1892) in his poem Lilian (1830) in which he describes Lilian as being airy fairy, dainty and delicate in her movements. Before this, from the late 16th/early 17th century, the word airy, on its own, meant flippant, unsubstantial or assuming graces.