For the public good, now usually with the implication of no financial recompense. Also occasionally attributive or as adjective Compare "pro bono [adjective]".
Also used on an open letter to a newspaper in place of the author's name.
Mid 17th century; earliest use found in Henry Parker (1604–1652), political writer. From post-classical Latin pro bono publico for the public good from classical Latin prō + bonō, ablative of bonum, use as noun of neuter of bonus + pūblicō, ablative of pūblicus.