1969, back-formation from remediation. Related: Remediated; remediating.
1540s, "divide in two equal parts," probably a back-formation from mediation or mediator, or else from Latin mediatus, past participle of mediare. Meaning "act as a mediator" is from 1610s; that of "settle by mediation" is from 1560s. Related: Mediated, mediates, mediating.