1) It sets things apart 2) One who quarantines 3) Quarantine imposer 
[microwave] An isolator is a two-port device that transmits microwave or radio frequency power in one direction only. It is used to shield equipment on its input side, from the effects of conditions on its output side; for example, to prevent a microwave source being detuned by a mismatched load. ==Non-reciprocity== To achieve non-reciproci...
• (n.) One who, or that which, isolates.
(from the article `germfree life`) ...The embryos of mammals are normally bacteriologically sterile, and germfree young can be obtained by cesarean operation, under germfree ...
a two-port device having much greater attenuation in one direction of propagation than in the opposite directiona two port device having much greater attenuation in one direction of propagation than in the opposite direction NOTE - An isolator is often used to prevent return reflections along a transmission path.
A two part component having greater attenuation in one direction than the other often used to prevent return reflections in a transmission path.
I'so·la`tor (ī'so*lā`tẽr or īs'o*lā`tẽr) noun One who, or that which, isolates.