1. entomology the host on which the sexual form is found in those insects with alternating sexual and parthenogenic generations 2. in rust fungi the sexual or telial host —note the pycnia and aecia of primary hosts form on the alternate or secondary host —see aecium, pycnium 3. in common (usually incorrect) usage with rust fungi the economically important host 4. the principal hostThis definition last updated 08/04/2008