n. any microscopic particle less than about 100 nanometers (nm) in diameter. In aerosol science, the term is often reserved for particles less than 50 nm in diameter; the term "ultrafine particles" is used for particles less than 100 nm in diameter.
Word Usage
"Researchers at International Business Machines Corp. said they developed a tiny drug, called a nanoparticle, that in test-tube experiments showed promise as a weapon against dangerous superbugs that have become resistant to antibiotics."