The Collaborative International Dictionary
Supererogate
Supererogate \Su`per*er"o*gate\, v. i. [imp. & p. p. Supererogated; p. pr. & vb. n. Supererogating.] [L. supererogatus, p. p. of supererogare to spend or pay out over and above; super over, above + erogare to expend or pay out money from the public treasury after asking the consent of the people. See Super-, and Erogate, Rogation.] To do more than duty requires; to perform works of supererogation; to atone (for a dificiency in another) by means of a surplus action or quality.
The fervency of one man in prayer can not supererogate
for the coldness of another.
--Milton.
Wiktionary
supererogate
vb. To engage in supererogation.