"Metre" or "Meter"?

Are they the same word or is there a difference?

• A "meter" is an instrument that measures something like gas, electricity, water, parking, etc. A thermometer measure temperature, a speedometer measures speed, a water meter measure water, etc.

• A "metre" is a unit of length. The ending metre is used for all lengths based on the metre: kilometre, centimetre, milimetre, etc.

Don't let the following confuse you!

The Americans use the word meter where the English use metre.