n. Symbol Rf
An artificially produced radioactive element with atomic number 104 that has only been produced in trace amounts. The isotope with mass number 261 has the longest confirmed half-life (65 seconds), although isotopes with longer half-lives have been reported. See Periodic Table.
[After Ernest Rutherford.]
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Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.