diminutive - dim-IN-you-TIV - tiny, small, pint-sized, petite, Lilliputian
Example: "Electrons are diminutive, even smaller than atoms, around which they orbit."
As a starter: and as a former teacher in English, I hope to add to reader's vocabulary by presenting a word a day in simple terms that anyone can understand - from current use in publications, radio,TV, etc. Remember: use a new word three times in a day and it's yours forever!