Definition of "velum"

a thin membrane resembling a veil or curtain, such as:

1. (anatomy) the soft palate  examples

2. (botany) a thin membrane partially covering the cluster of sporangia near the leaf base in quillworts and their extinct relatives  examples

3. (mycology) a veil-like membrane of immature mushrooms extending from the margin of the cap to the stem and is torn by growth, to reveal the gills

4. (malacology) a locomotory and feeding organ provided with cilia found in the larval stage of bivalves

5. (zoology) a annular membrane, typically bordering a cavity, especially in certain molluscs, medusae, and other invertebrates

6. a delicate membrane found on certain protists  examples

(meteorology) an accessory cloud resembling a veil extending over a large distance; normally associated with cumulus and cumulonimbus