The term HOME FOR PROTONS can be solved by the crossword solution ATOM, which is a four-letter word. An ATOM is the smallest unit of matter that retains its chemical properties. Atoms are composed of protons, neutrons, and electrons, with protons being the positively charged particles located in the nucleus of an ATOM. Therefore, the term HOME FOR PROTONS can be interpreted as the nucleus of an ATOM, which is the home for protons.