The Collaborative International Dictionary of English v.0.48:
May \May\ (m[=a]), v. [imp. Might (m[imac]t)] [AS. pres. maeg
I am able, pret. meahte, mihte; akin to D. mogen, G.
m["o]gen, OHG. mugan, magan, Icel. mega, Goth. magan, Russ.
moche. [root]103. Cf. Dismay, Main strength, Might. The
old imp. mought is obsolete, except as a provincial word.]
An auxiliary verb qualifying the meaning of another verb, by
(a) Ability, competency, or possibility; -- now oftener
expressed by can.
How may a man, said he, with idle speech,
Be won to spoil the castle of his health!
For what he [the king] may do is of two kinds; what
he may do as just, and what he may do as possible.
For of all sad words of tongue or pen
The saddest are these: "It might have been."
(b) Liberty; permission; allowance.
Thou mayst be no longer steward. --Luke xvi. 2.
(c) Contingency or liability; possibility or probability.
Though what he learns he speaks, and may advance
Some general maxims, or be right by chance. --Pope.
(d) Modesty, courtesy, or concession, or a desire to soften a
question or remark.
How old may Phillis be, you ask. --Prior.
(e) Desire or wish, as in prayer, imprecation, benediction,
and the like. "May you live happily." --Dryden.
May be, & It may be, are used as equivalent to
possibly, perhaps, maybe, by chance,
peradventure. See 1st Maybe.