fertiliser fer·ti·li·ser rare uk noun 1. any substance such as manure or a mixture of nitrates used to make soil more fertile Synonymsfertilizerplant food Related words Word family fertilize Broader terms chemical Narrower terms organic Part of sodium nitratepotassium nitrateammonium nitrate WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.