In early use: †that aids or rescues from harm (obsolete ). Later: that gives help or support by subvention, or as a subvention.
In 19th cent. specifically designating charity in the form of subsidies and relief intended to provide immediate aid to those in need (often opposed to preventive charity, which addressed the causes of deprivation). Now historical ..
Origin
Late 17th century; earliest use found in Richard Strange (c1611–1682), Jesuit. From subvent or its etymon classical Latin subvent-, past participial stem of subvenīresubvene + -ive.