a combining form with the meaning “very small, minute,” used in the formation of compound words (nanoplankton); in the names of units of measure it has the specific sense “one billionth” (10-9): nanomole; nanosecond. Also,nanno-; esp. before a vowel,nan-. Also,nanno-; esp. before a vowel,nan-.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.