semi-permeable

adjective

1. permeable only to certain small molecules: a semipermeable membrane.

adjective

1. (esp of a cell membrane) selectively permeable

adj.1873, from semi- + permeable. Translating German halbdurchlässig. adj.

1. Partially permeable.
2. Allowing passage of certain, especially small, molecules or ions but acting as a barrier to others. Used of biological and synthetic membranes.