- any of various algaelike fungi constituting the phylum Oomycota of the kingdom Fungi (or the class Oomycetes of the kingdom Plantae), characterized by the formation of oospores.
- any organism of the phylum Oomycota (or Oomycetes), formerly classified as fungi but now usually included in the kingdom Protoctista or Protista : includes the water moulds and downy mildews
