2. A land area of uniform elevation: "The pictures were hung on the wall at eye level."
3. Etymology: The Latin word for a "balance" or "scales" was libra. English took it as The zodiacal sign and it lies behind many terms for units of measurement, including litre, or liter and the abbreviation lb or £ for British currency known as the "pound".
Its diminutive form was libella, which denoted an "instrument for checking horizontally" and hence a "horizontal line".
It passed into Old French as livel; which in modern French has become niveau, "level", and it entered English as level.
2. To render people or things equal; to equalize: "The mayor wants to level the opportunities for smaller companies to compete against the big companies in the city."
3. To direct something against a person or group: "Several complaints have been leveled against the government for not responding to the economic crisis that is causing so many people to lose their jobs."
4. To speak honestly to someone: "Rebecca's co-worker never leveled with her about backing his car into her vehicle in the parking lot."
2. Thriving on several parallel layers of material arranged one on top of another.
There are four BSLs, with BSL-4 requiring the highest level of security.
The vials are filled with liquid, and an air bubble is left to aid in the determination of the horizontal plane and highest vertical point.