Late 15th century (in an earlier sense). As adjective from classical Latin adiectus; as noun partly from post-classical Latin adiectum addition, adjective, and partly shortened from adjective (originally as a graphic abbreviation).

Late 15th century (in an earlier sense). From classical Latin adiect-, past participial stem of adiicere (also adicere) to throw at or towards, to direct or aim towards, to attach, affix, to add, to contribute, to associate, to add in speech or writing, to annex from ad- + iacere to cause to lie, to lay, to throw.