Some call it the beginning of summer and drive the cattle up to summer pasture.  Here in New Hampshire I’ve seen snow in May on at least a handful of occasions.  this word is found hyphenated or as a single word in OED.

• 19.012 Merry is May-time, and merry our meeting.
• 19.020 Merry is May-time!’

“May, n.2.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/115285. Accessed 19 September 2017.