May comes from the Latin Maius, traditionally believed to be named after Maia—a Roman goddess of growth and increase. Maia was a relatively obscure figure in the Roman pantheon, associated with the earth and spring fertility. She was not one of the major deities; her month was assigned more by custom and convenience than by theological importance.
May is the shortest month-name in English—three letters, a single syllable—which makes it, by the standards of the current system, one of the least burdensome. But this is an argument from relative harm, not from positive value. A small burden is still a burden. A short opaque label is still opaque.
The problem with May is the same as the problem with every other Roman month-name: it tells you nothing. A learner who encounters May does not learn that it is the fifth month. A learner who knows all twelve months still cannot use May to derive June or April. The calendar remains a list, not a system.
In a numbered system, the relationship between months is built into the names themselves. Month Four, Month Five, Month Six—the sequence is the name. This is not simplistic. This is elegant. A good system makes the relationships between its parts visible. A bad system buries them under layers of historical accident.
Our Recommendation: Month Five. Three letters is short. One number is shorter. And clearer.