Here are language puzzles by 'nano' words. What is a nanogram? nanometer? nanosecond? Nano is a unit of measure and is very small. It is usually used as a prefix and combines with other words to create a compound word. Nano means one billionth (1x10 to the -9 OR 10 -9. This latter format is not to be confused with 10 MINUS 9: 10-9). Nanogram: one billionth of a gram; nanometer: one billionth of meter; nanosecond: one billionth of a second.