Donation, benefaction, contribution, alms are comparable when they denote a gift of money or its equivalent for a charitable, philanthropic, or humanitarian object.
Donation is freely used for such a gift. It may, however, retain in this sense some feeling of its earlier meaning of the act or right (as of a state, a ruler, or a patron) of granting or giving to a subordinate (as a subject or a client) and is, therefore, the normal term to apply to a gift of substantial value, presented more or less publicly, and usually without reference to other givers or gifts.
Benefaction is often used in place of donation, especially when there is the intent to compliment the donor and to imply his benevolence or the beneficence of his gift. The latter, however, is the basic implication and the word may be appropriately used of any benefit conferred or received whether it has money value or not.
Contribution implies participation in giving; it is applicable to small as well as large amounts of money; it is the modest term which one may apply to his own gift, though others may rightly call it a donation or benefaction.
Alms implies the aim of relieving poverty either in former times as the fulfillment of a religious obligation or as a practical manifestation of the virtue of charity or in more recent times as an indication of casual benevolence displayed chiefly in the giving of petty sums to beggars or paupers.