Pronunciation: (i-pis'tu-sis),[key] —n., —pl.-sesPronunciation: (-sēz").[key] 1. Genetics.a form of interaction between nonallelic genes in which one combination of such genes has a dominant effect over other combinations.
2. Med. a. the stoppage of a secretion or discharge.
b. a scum that forms on a urine specimen upon standing.