may

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A hawthorn or its blossoms.
• auxiliary verb To be allowed or permitted to.
• auxiliary verb Used to indicate a certain measure of likelihood or possibility.
• auxiliary verb Used to express a desire or fervent wish.
• auxiliary verb Used to express contingency, purpose, or result in clauses introduced by that or so that.
• auxiliary verb To be obliged, as where rules of construction or legal doctrine call for a specified interpretation of a word used in a law or legal document.

from The Century Dictionary.

• noun A maiden; a virgin.
• To celebrate May-day; take part in the festivities of Mayday: chiefly or only in the verbal noun maying and the derivative mayer: as, to go a maying.
• A. As an independent verb, or as a quasi-auxiliary: To have power; have ability; be able; can.
• To indicate possibility with contingency.
• In this sense, when a negative clause was followed by a contingent clause with if, may in the latter clause was formerly used elliptically, if I may meaning ‘if I can control it’ or ‘prevent it.’
• Sometimes may is used merely to avoid a certain bluntness in putting a question, or to suggest doubt as to whether the person to whom the question is addressed will be able to answer it definitely.
• The preterit might is similarly used, with some slight addition of contempt.
• To indicate opportunity, moral power, or the absolute power residing in another agent.
• In this sense may is scarcely used now in negative clauses, as permission refused amounts to an absolute prohibition, and accordingly removes all doubt or contingency.
• To indicate desire, as in prayer, aspiration, imprecation, benediction, and the like. In this sense might is often used for a wish contrary to what can or must be: as, O that I might recall him from the grave !
• In law, may in a statute is usually interpreted to mean must, when used not to confer a favor, but to impose a duty in the exercise of which the statute shows that the public or private persons are to be regarded as having an interest.
• In conditional clauses. [Rare, except in clauses where permission is distinctly expressed.]
• In concessive clauses.
• In clauses expressing a purpose.
• noun The fifth month of the year, consisting of thirty-one days, reckoned on the continent of Europe and in America as the last month of spring, but in Great Britain commonly as the first of summer.
• noun Figuratively, the early part or springtime of life.
• noun [lowercase] The hawthorn: so called because it blooms in May. Also May-bush.
• noun Some other plant, especially species of Spiræa: as, Italian may.
• noun The festivities or games of May-day.
• noun In Cambridge University, England, the Easter-term examination.
• noun A kinsman.
• noun A person.

from the GNU version of the Collaborative International Dictionary of English.

• verb Ability, competency, or possibility; -- now oftener expressed by can.
• verb Liberty; permission; allowance.
• verb Contingency or liability; possibility or probability.
• verb Modesty, courtesy, or concession, or a desire to soften a question or remark.
• verb Desire or wish, as in prayer, imprecation, benediction, and the like.
• verb are used as equivalent to possibly, perhaps, maybe, by chance, peradventure. See 1st Maybe.
• noun obsolete A maiden.
• noun The fifth month of the year, containing thirty-one days.
• noun The early part or springtime of life.
• noun (Bot.) The flowers of the hawthorn; -- so called from their time of blossoming; also, the hawthorn.
• noun The merrymaking of May Day.
• noun (Bot.) a shrubby species of Spiræa (Spiræa hypericifolia) with many clusters of small white flowers along the slender branches.
• noun (Bot.) the fruit of an American plant (Podophyllum peltatum). Also, the plant itself (popularly called mandrake), which has two lobed leaves, and bears a single egg-shaped fruit at the forking. The root and leaves, used in medicine, are powerfully drastic.
• noun (Zoöl.) any one of numerous species of large lamellicorn beetles that appear in the winged state in May. They belong to Melolontha, and allied genera. Called also June beetle.
• noun the first day of May; -- celebrated in the rustic parts of England by the crowning of a May queen with a garland, and by dancing about a May pole.
• noun the morning dew of the first day of May, to which magical properties were attributed.
• noun (Bot.) a plant that flowers in May; also, its blossom. See Mayflower, in the vocabulary.
• noun (Zoöl.) any species of Ephemera, and allied genera; -- so called because the mature flies of many species appear in May. See Ephemeral fly, under Ephemeral.
• noun any May-day sport.
• noun the queen or lady of May, in old May games.