1A membrane or membranous structure, typically covering another structure or partly obscuring an opening.

1. 1.1Anatomy The soft palate.
   Example sentencesExamples

   • For ‘mouth breathing’ protocols, patients were instructed with a technique aimed at achieving velum closure of the nasopharynx and asked to practice it prior to testing.
   • This technique allows for closure of the velum, thus excluding nasal NO contamination during expiration.
   • The back of the tongue lies opposite the soft palate or velum when the tongue is in a state of rest, and sounds made with the back include velar consonants and back vowels.
2. 1.2Zoology A membrane, typically bordering a cavity, especially in certain molluscs, medusae, and other invertebrates.
   Example sentencesExamples

   • This fact, together with the fragility of the velum, may cause problems for identification of growth stage and sex of the particular specimen.
   • Adult heteromorphs show wide velum; the velum in tecnomorphs is narrower.
   • Its multispiral, heavily sculptured, darkly colored shell, plus its large four-lobed velum, point to a different type of snail, one of the neogastropods.
   • Scyphozoan medusae differ from those of hydrozoans in lacking a velum.
   • Free-living medusoid hydrozoans can be hard to tell from scyphozoans, but hydrozoan medusae generally have a muscular shelf, or velum, projecting inward from the margin of the bell.
3. 1.3Botany The veil of a toadstool.