semipermeable

The word is a modern scientific compound, built from classical elements to describe a specific physical property. The prefix "semi-", from Latin, introduces the concept of partiality or selectivity. It is attached to "permeable", an adjective of Latin origin describing the capacity for substances to flow through a material. Thus, the literal construction "half-permeable" logically evolved into the modern, more precise meaning of selectively allowing passage to some molecules while blocking others, a concept central to chemistry and biology.

Structure: semi (half) + permeable (allowing passage) semi: From Latin sēmi- meaning "half". A prefix indicating partiality or incompleteness. permeable: From Latin permeābilis, from permeāre (to pass through), from per- (through) + meāre (to go, pass). An adjective meaning allowing liquids or gases to pass through.