We don't have synonyms for free radicals yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are free radical.
(n) :
(chemistry, physics) A molecule, ion or atom that has one or more unpaired electrons, and which is generally highly reactive (and therefore often occurs only as a transient species).
(n) :
(chemistry, physics) A molecule, ion or atom that has one or more unpaired electrons, and which is generally highly reactive (and therefore often occurs only as a transient species).