spirit level 
noun
A device consisting of a sealed glass tube partially filled with alcohol or other liquid, containing an air bubble whose position reveals whether a surface is perfectly level.Bricklaying tools include a hammer, mason's string, a few 10d nails, a trowel, a spirit level, a hand level, a piece of carpenters chalk and a broad-bladed cold chisel....
- A single tool - technically called a spirit level, better known simply as a level - is the workhorse in the industry for checking plumb and level, and a good spirit level belongs in every toolbox.
- It is used to square the end of a board, mark a 45-degree angle for mitering, and even make quick level checks with the built-in spirit level.