1) An act of subjoining 2) Expanding upon 3) Expansion 4) Something subjoined 5) Subjoining 6) Supplementation 7) The act of supplementing 8) The state of being subjoined Found on https://www.crosswordclues.com/clue/subjunction
Sub·junc'tion noun [ See Subjunctive .] 1. Act of subjoining, or state of being subjoined. 2. Something subjoined; as, a subjunction to a sentence. Found on http://www.encyclo.co.uk/webster/S/223