n. pl. fre·nums or fre·na (-nə)
A membranous fold of skin or mucous membrane that supports or restricts the movement of a part or organ, such as the small band of tissue that connects the underside of the tongue to the floor of the mouth.
[Latin frēnum, bridle, from frendere, to grind; see ghrendh- in the Appendix of Indo-European roots.]
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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.