free-radical

The term 'free-radical' is a modern scientific compound from the mid-20th century. It combines 'free', in its sense of being unbound or independent, with 'radical', a chemical term for a fundamental group of atoms that normally exists as part of a stable molecule. The 'free' specifies that this radical is not bound within a larger structure but exists independently with an unpaired electron, making it highly reactive. The logic of the term thus directly describes its key chemical characteristic: a fundamental reactive group existing in an unattached, unstable state.

Structure: free (unbound) + radical (fundamental group) - free: From Old English frēo (not in bondage, acting of one's own will). In this compound, it functions as an adjective meaning 'unattached', 'unbound', or 'independent'. - radical: From Late Latin radicalis (of or having roots), from Latin radix (root). In chemistry, it functions as a noun meaning a group of atoms forming a fundamental constituent of a molecule.