(ethics,medicine) To perform no actions which will be injurious or in any way unfavorable to another person, regardless of whether one does anything of positivebenefit for that other person.
A doctor's principle code is, "First, do no harm."
2012, A. Bame Nsamenang (ed.), Handbook of African Educational Theories and Practices, ISBN 9789956444649, p. 100 (Google preview):
Hence, some people consider non-maleficence to be the most basic of all the cardinal principles of ethics; it lays down the least minimum condition for ethical correctness, as if to say: "even if you would not do good, at least do no harm."