Definition of "May"

All in the merry month of May, / When green leaves they was springing, / This young man on his death-bed lay, / For the love of Barbara Allen.

Before 1789, "Bonny Barbara Allen," traditional ballad, collected in Francis James Child and George Lyman Kittridge (1886), The English and Scottish Popular Ballads, vol. II, part II, p. 277

[…] I will not send Owen's Lily May to the almshouse." "Lily―what?" demanded Mrs. Morley rather sharply, for she was half provoked with what she mentally called Amy's whim of keeping the outcast child when she might send it to the asylum. "Lily May," said Amy, smiling. "Her name is Mary, and we called her first Little Mary, and then Little May. But Owen calls her Lily May."

1856, E. D. E. N. Southworth, The Widow's Son, T. B. Peterson, published 1867, page 210

Their parents named them June and May because their birthdays occurred in those months. […] May was like the time of year in which she had been born, changeable, chilly and warm by turns, sullen yet able to know and show loveliness that couldn't last.

1982, Ruth Rendell, The Fever Tree and Other Stories, Hutchinson, page 119

It's an awkward name: Isamay, pronounced Is-a-may. Isa is my paternal grandmother's name (shortened from Isabel) and May my maternal grandmother's (it comes, somehow, from Margaret). The amalgamation is, as you see, strictly alphabetical. Life, I feel, would have been much easier if they had chosen Maybel.

2010, Margaret Forster, Isa & May, Chatto & Windus, page 5