Supererogatory, gratuitous, uncalled-for, wanton are comparable when they mean given or done freely and without compulsion or provocation or without warrant or justification.
Supererogatory basically implies a giving above or beyond what is required or is laid down in the laws or rules; the word then suggests a devotion or loyalty that is not satisfied merely with the doing of what is required and that finds expression in the performance of additional labors, works, or services beyond those expected or demanded.
In other usage the term is definitely depreciative in that it implies not a giving freely over and above what is required but a giving or adding of what is not needed or wanted and is therefore an embarrassment or encumbrance.
Gratuitous may apply to a giving voluntarily without expectation of recompense, reward, or compensation <the gratuitous education provided by the public schools of the United States> but it often stresses a giving without provocation of something disagreeable, offensive, troublesome, or painful.
Gratuitous often means little more than uncalled-for , which suggests not only a lack of provocation but a lack of need or justification and therefore implies impertinence or absurdity, often logical absurdity.
Wanton (see also LICENTIOUS ) also implies want of provocation, but it stresses capriciousness and the absence of a motive except reckless sportiveness or arbitrariness or pure malice.