A stock fund is a type of investment fund that invests primarily in stocks and other equity securities. Synonyms for stock fund include equity fund, mutual fund, investment fund, and index fund. Equity fund refers to a type of investment fund that focuses on equity securities. Mutual fund is a professionally-managed investment fund that pools money from many investors to purchase securities. Investment fund is a broad term that includes different types of funds, including stock funds. Index fund is a type of mutual fund or exchange-traded fund (ETF) that tracks the performance of a specific market index. In summary, these synonyms refer to different types of investment funds that invest in stocks and equity securities.