After the death of Wohler's wife, Liebig invited Wohler to collaborate with him in Giessen. The result of their work was the recognition of the benzoyl radical (C7H5O). [In the first half of the 19th century their was little agreement on the mass of carbon (6 or 12) and oxygen (8 or 16). The formula is the modern version.] This unit was believed to be unalterable, functioning as an electropositive element does in the inorganic world. Radical in the early 19th century did not mean what it means in the late 20th century.
At the turn of the century, when "free radicals" were finally detected having an unpaired electron, the "free" was added to distinguish it from the older nomenclature. Although the term free radical is still used today, the term radical is used frequently because the older use of radical is only of historical interest.