Subsidiary comes from Latin subsidiārius ('serving as reserve, auxiliary'), from subsidium ('support, reserve troops, help'), from sub- ('under, behind') + sedēre ('to sit'). The historical chain includes Latin sub, Latin sedēre, and Proto-Indo-European *sed-. The quoted older senses, "serving as reserve, auxiliary", "support, reserve troops, help", "under, behind", and "to sit", supply the semantic anchors for subsidiary. The formation is best read as compound and borrowed: the word subsidiary carries its older form-history into a compact English lexical shape. In present English it is used as a noun, "a company controlled by another; of secondary importance". English derivatives include subsidiarily and subsidiarity; related English forms include subsidy, subsidize, reside, and preside. The result is a noun and adj whose etymology preserves both the older form and the later English specialization.