The term 'PARTICLE SMALL' can be solved by two crossword solutions: ATOM (4 letters) and MOLECULE (8 letters). An ATOM is the smallest particle of an element that still retains its chemical properties. Atoms are composed of protons, neutrons, and electrons. A MOLECULE is a group of two or more atoms held together by chemical bonds. Molecules can be composed of different types of atoms, and they can vary in size and complexity.