semipermeable
adjective
semi·per·me·able
| \ ˌse-mē-ˈpər-mē-ə-bəl
, ˌse-ˌmī-, -mi-\
, ˌse-ˌmī-, -mi-\
Definition of semipermeable
: partially but not freely or wholly permeable
specifically
: permeable to some usually small molecules but not to other usually larger particles
a semipermeable membrane