Wordnet 3.0
NOUN (1)
1. 
 a thin membrane (a double layer of lipids) enclosing the cytoplasm of a cell; 
 proteins in the membrane control passage of ions (like sodium or potassium or calcium) in and out of the cell; 
- Example: "all cells have a cell membrane"[syn: cell membrane, cytomembrane, plasma membrane]
WordNet (r) 3.0 (2006):
cytomembrane
    n 1: a thin membrane (a double layer of lipids) enclosing the
         cytoplasm of a cell; proteins in the membrane control
         passage of ions (like sodium or potassium or calcium) in
         and out of the cell; "all cells have a cell membrane" [syn:
         cell membrane, cytomembrane, plasma membrane]