There are many synonyms for the word "compost," which is a mixture of organic matter that is used as fertilizer for plants. One of the most common synonyms for compost is "mulch," which refers to a similar mixture of organic materials like leaves, grass clippings, and twigs that is used to cover the soil to enrich it. Another synonym for compost is "humus," which refers to the rich, dark soil-like substance that forms as a result of decomposed organic matter. Other synonyms for compost include "manure," "organic fertilizer," "worm castings," and "soil amendment." All of these synonyms refer to materials that are used to improve soil quality and promote plant growth.