1. To receive information from one's surroundings through the body's nerves and other physical organs: Sitting quietly by the side of the river, Melony was able to sense the change in the wind and decided she should go home before it started to rain.

While Mark was walking home from the bus, he sensed a movement behind him which happened to be his daughter who was trying to catch up with him after getting off a different bus.

2. To detect and to identify a change in something: The store's device at the back senses when the door is opened at night and sounds the alarm.
3. Etymology: from Latin sensus, "feeling, perception"; from sens-, past participle stem of sentire, "to feel".

An electrode in which a gas-permeable membrane of the body separates the test solution from an aqueous electrode solution in contact with an ion-selective electrode.

Gas permeation of the membrane changes the chemical equilibrium within the electrolyte, and the ion-sensitive electrode detects this change.